on the cranial osteology of chiroptera. i. pteropus

ON THE CRANIAL OSTEOLOGY OF

CHIROPTERA. I. PTEROPUS

(MEGACHIROPTERA: PTEROPODIDAE)

NORBERTO P. GIANNINI

Division of Vertebrate Zoology (Mammalogy),

American Museum of Natural History

([email protected])

JOHN R. WIBLE

Section of Mammals, Carnegie Museum of Natural History,

5800 Baum Boulevard, Pittsburgh, PA 15206

([email protected])

NANCY B. SIMMONS

Division of Vertebrate Zoology (Mammalogy),

American Museum of Natural History

([email protected])

BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY

CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024

Number 295, 134 pp., 50 figures

Issued January 12, 2006

Copyright E American Museum of Natural History 2006 ISSN 0003-0090

CONTENTS

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Material and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5The Skull as a Whole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Regions of the Skull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Rostral View of the Skull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Dorsal Surface of the Skull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Lateral Surface of the Skull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Ventral Surface of the Skull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16Caudal Surface of the Skull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

The Skull Bones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Rostral Bones (ossa faciei) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Nasal. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Premaxilla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Maxilla . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Ventral Nasal Concha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Palatine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Lacrimal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Jugal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Cranial Bones (ossa cranii). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Frontal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Parietal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Interparietal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Pterygoid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Vomer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Sphenoid Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Squamosal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Petrosal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35Entotympanic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Ectotympanic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Middle Ear Ossicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Occipital Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Mandible . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Posterior Branchial Skeleton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Hyoid Apparatus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49Larynx. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Internal Surfaces of the Skull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Nasal Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Premaxillary Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Maxillary Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Palatine Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56Fronto-Ethmoidal Surfaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57Presphenoid Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61Basisphenoid Surface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61Parietal Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63Squamosal Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65Occipital Surface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

Foramina Contents and Homology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70Dentition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

Permanent Dentition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88Deciduous Dentition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

2

Skull Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99Shape Change . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99Sequence of Bone Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107Skull Shape in Adult Megachiropterans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107Interspecific Suture Variation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108Internal Surfaces of the Skull . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109Foramina. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111Dentition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

Directions for Future Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115Appendix 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120

List of Anatomical Terms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120Appendix 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132

List of Anatomical Abbreviations Used in Figures. . . . . . . . . . . . . . . . . . . . . . . . . 132

2006 GIANNINI ET AL.: CRANIAL OSTEOLOGY OF PTEROPUS 3

ABSTRACT

Although detailed anatomical descriptions of skull morphology are available for representa-tives of many mammalian orders, no such descriptive work exists for bats, a group thatcomprises over 20% of extant mammalian species. In this paper, we provide a detaileddescription of the skull of Pteropus (Mammalia: Chiroptera: Megachiroptera: Pteropodidae)and establish a system of cranial nomenclature following the Nomina Anatomica Veterinaria.Based on a series of specimens of Pteropus lylei, we describe the skull as a whole and themorphology of external surfaces of 24 bones (7 rostral, 16 cranial, plus the mandible) and 17teeth. We describe internal surfaces and additional bones of disarticulated skulls of Pteropuslivingstonii and use material from the same species to describe the middle ear ossicles and thepetrosal bone. We include a description of the hyoid apparatus and larynx based on Pteropustonganus and a description of the deciduous dentition based on Pteropus hypomelanus. Usinga sectioned fetus, we determine the content and homology of all cranial foramina present in theskull of Pteropus. We outline the ontogenetic changes from newborn pups to adults, consideringchanges in skull shape and the sequence of bone fusion and tooth eruption. Based on selectedcomparisons to other megabats, we discuss broad patterns of variation in general cranial shape,and interspecific variation in sutures, foramina, processes, and dentition. Overall, this workestablishes a descriptive and nomenclatorial benchmark for chiropteran skull anatomy in linewith similar works in other mammalian orders, with the aim of creating common ground forcomparative, phylogenetic, and functional studies of the bat skull, including comparisons withother mammals.

INTRODUCTION

Detailed studies of skull morphology ofselected fossil and living mammals havegenerated a solid basis of description andnomenclature for comparative functionalanalyses, systematic studies, and phylogeneticanalyses of a number of mammalian clades.Examples include early Tertiary leptictidinsectivorans (Novacek, 1986), the Paleocenemetatherian Pucadelphys (Marshall and Mui-zon, 1995), the Late Cretaceous multituber-culate Kryptobaatar (Wible and Rougier,2000), the Late Cretaceous eutherian Za-lambdalestes (Wible et al., 2004), the extantshort-tailed opossum Monodelphis (Wible,2003), and the extant yellow armadilloEuphractus (Wible and Gaudin, 2004). Al-though bats comprise over 20% of extantmammalian species (Simmons, 2005), nosuch detailed anatomical study of a bat skullhas been completed to date. Some studieshave investigated a portion of the bat skull indetail—such as works on the ear region(Henson, 1961, 1970; Novacek,1985a,1985b, 1987, 1991; Wible and Davis, 2000),the ethmoid region (Bhatnagar and Kallen,1974; Kamper and Schmidt, 1977), and thehyoid apparatus (Sprague, 1943)—but theskull as a whole has never been subject toa comprehensive anatomical treatment. Be-

cause alpha-level systematics and morpholo-gy-based phylogenetics of mammals tendto rely heavily on craniodental characters,lack of a standardized reference for batshas made communication about bat skullmorphology difficult and has impededcomparative studies with other mammals.Several new bat species are described everyyear (Simmons, 2005), some of which arenew megachiropterans (e.g., Maryanto andYani, 2003), and it is important that thedetails of their morphology be adequatelycommunicated to the scientific community.Molecular studies are increasingly identifyingcryptic species that are difficult to distinguishmorphologically (e.g., Ruedi and Mayer,2001; Mayer and von Helversen, 2001;Campbell et al., 2004), making precision inanatomical terminology all the more impor-tant. Increasingly sophisticated functionalstudies of feeding behavior (e.g., Dumont,1999, 2003; Nicolay and Dumont, 2000) andevolutionary relationships (e.g., Simmonsand Geisler, 1998, 2002; Gunnell and Sim-mons, in press) similarly require more de-tailed information on skull morphology andelement homology. As the diversity of batscontinues to be unveiled, the need forstandardized frames of reference for describ-ing and analyzing bat cranial morphologywill only increase.

4

The aim of our work is to providea detailed description of the skull of a repre-sentative of Chiroptera, in this case a mega-chiropteran, that will help fill the vacuum ofanatomical description for bats. This repre-sents a special challenge because adult batsare characterized by relatively completefusion of cranial bones. Thus, ontogeneticconsiderations are fundamental to under-standing the structure of individual bones,relationships among different bones, loca-tions of contacts between elements, and theexact placement of structures such as foram-ina and processes. We chose to focus ourstudy on the megachiroptean bat Pteropusbecause these animals are relatively large, arewell represented in museum collections, andare commonly cited in the comparativeliterature on bats. The foundation of ourunderstanding of megachiropteran systemat-ics was provided by Andersen (1912), whoused many cranial features in his character-izations of subfamilies, genera, and species inthe family Pteropodidae. Much of the termi-nology subsequently applied to pteropodidcrania (e.g., by Bergmans, 1976, 1977, 1980,1988, 1989, 1990, 1994, 1997, 2001; Bergmansand Rozendaal, 1988; Koopman, 1989, 1994;and others) was derived from Andersen’s(1912) work. However, neither he nor anysubsequent author provided a detailed de-scription of the megachiropteran skull, andterminology has not been uniformly applied,even within this relatively restricted family.Here we provide a detailed anatomical de-scription of the skull of Pteropus. Thisdescription includes the skull as a whole,the external surfaces of each bone as theyappear in intact skulls, the internal surfacesof bones as they appear in disarticulatedskulls, the dentition, and the contents of allcranial foramina. We provide a terminologyconsistent with the Nomina AnatomicaVeterinaria (NAV), as well as pertinentsynonyms from the bat literature and exten-sions to cases not covered by the NAV.

MATERIAL AND METHODS

TAXONOMIC SAMPLE: Pteropus is one ofthe most speciose genera of bats, including 67currently recognized species representing 18species groups (Simmons, 2005). Andersen

(1912) described three skull types in Pteropususing P. hypomelanus, P. anetianus, and P.scapulatus as models. Andersen (1912) con-sidered P. hypomelanus as representative ofthe genus because it lacks obvious specializa-tions such as a short rostrum associated withheavy teeth (characteristic of the anetianustype) or an excessively weak cheek toothdentition (scapulatus type). Andersen (1912)viewed these specialized forms as occupyingthe ends of a gradient; most Pteropus speciesfit in between, associated with the relativelyunmodified hypomelanus type near the mid-dle of the gradient. Our studies focused oncomparatively unspecialized Pteropus specieswith hypomelanus-type skulls sensu Andersen(1912).

We chose Pteropus lylei K. Andersen, 1908(vampyrus species group) as the principalsubject of our descriptions on the basis of theavailability of a beautifully preserved seriesof young adults housed at the CarnegieMuseum of Natural History (CM), comple-mented by a collection at the AmericanMuseum of Natural History (AMNH, seebelow). We also examined comparativematerial from other megachiropteran specieshoused at those museums and at the Museumof Natural History, London (BMNH), theField Museum of Natural History, Chicago(FMNH), the Royal Ontario Museum, Tor-onto (ROM), and the United States NationalMuseum of Natural History, SmithsonianInstitution, Washington, DC (USNM). Weinclude descriptions of Pteropus capistratus(personatus species group), Pteropus living-stonii (livingstonii species group), and Pter-opus hypomelanus (subniger species group) inorder to treat aspects of the skull anatomythat were not accessible to examination inour specimens of P. lylei. Again, the selectionwas based on the suitability of specimens forthe descriptive tasks. In particular, featuresof the auditory region were studied in furtherdetail in P. livingstonii, whereas aspects ofskull growth and bone fusion were studied inP. lylei and P. capistratus. Newborn P.hypomelanus were used to describe the de-ciduous dentition. Specimens of Pteropusneohibernicus (neohibernicus species group)and Pteropus vampyrus (vampyrus speciesgroup) were also used for comparativepurposes.


ANATOMICAL SPECIMENS: Our descrip-tions are based primarily on CM 87972,a subadult male of Pteropus lylei fromThailand (Chon Buri Province). This speci-men has M2 and m3 only partially eruptedand most skull bones unfused (sutures clearlyvisible). The condylobasal length of CM87972 is 50.7 mm. Comparisons were fre-quently made with CM 87973, another sub-adult of the same series. Other specimensexamined included AMNH 30217, 217045,237593, 237594, 237595, 237596, 237598,237599, 240005, and 240006. Of these, twospecimens (AMNH 30217 and 217045) areold individuals with extreme tooth wear (seeDentition) and almost complete bone fusion,whereas two (AMNH 240005 and 240006)are much younger, at an age stage onlyslightly older than the Carnegie specimens.The remainder of the AMNH sample con-sisted of adults with fully erupted permanentteeth and varying levels of tooth wear andbone fusion. The specimen of Pteropuscapistratus (AMNH 194276) is a newbornpup with most deciduous teeth and nopermanent teeth erupted. The specimens ofPteropus livingstonii used for the additionaldescriptions of the auditory region andinternal surfaces of the skull were AMNH274466, 274477, and 274515. Additionalspecimens used occasionally for comparativepurposes included Pteropus neohibernicusAMNH 152402 and Pteropus vampyrusAMNH 198691.

THE HISTOLOGICAL SPECIMEN: Our his-tological observations are based on a 93.5-mm crown–rump length fetus of Pteropussp. cataloged as No. 831 in the DukeUniversity Comparative Embryological Col-lection, Durham, NC. The head was seriallysectioned in a frontal plane, with sectionthicknesses of 16 mm, and stained withMallory’s trichrome. The basicranial vascu-lature and anatomy of this specimenwere described by Wible (1992). Fordetailed descriptions of the chondrocraniaof pteropodids, the reader is referred toStarck (1943) and Jurgens (1963). Theformer describes a younger stage fetus ofPteropus seminudus (5 Rousettus lesche-naultii following Koopman, 1993), and thelatter describes a later stage fetus of Rouset-tus aegyptiacus.

DESCRIPTIONS ANDTERMINOLOGY: Basedon CM 87972, we describe the externalskull osteology in two main sections. Thesection on the skull as a whole includes anoverview of the skull regions, along withmore detailed descriptions of the rostral,dorsal, lateral, ventral, and occipital views.The bones of the skull are subsequentlydescribed one by one in more detail in thefollowing section. Names of general struc-tures of the skull are given in the firstsection in English with their equivalentLatin terminology from the fourth editionof the Nomina Anatomica Veterinaria(NAV, 1994) italicized and in parentheses:for instance, the glenoid fossa (fossa mandi-bularis). The Latin name is given at the mostrelevant (usually the first) mention. When theEnglish name corresponds with the Latinname, we italicize it once, at first use: forinstance, the foramen magnum.

In the section on the skull as a whole, wedescribe overall external aspects of bonystructures; descriptions in this section arenot intended to be exhaustive, and only themost conspicuous traits are treated. In thebone-by-bone section, we greatly increase thedetail of descriptions, also introducing somelevel of redundancy. Here we incorporate allspecific terminology directly related to eachbone (e.g., foramina, processes, borders,shapes, surfaces, and relationships with otherbones) with the same English (Latin) con-vention. We also include the NAV arthrolo-gical nomenclature, defining the articulationat first use and naming it in English (andLatin). For instance, the articulation betweenthe nasal and the frontal will be defined onceas the frontonasal suture (sutura frontonasa-lis) and described in the treatment of thenasal (later mentions of this suture are inEnglish). Often, reference is made to termi-nology used in cranial anatomy of the dogbased on Evans (1993), because the dog skullhas been described and illustrated in greatdetail.

We deal mainly with external surfaces andother structures that are externally visible inintact skulls. All bones are described in detailexcept for the ethmoid complex (mostlyhidden from view in intact skulls) and,partially, the vomer (whose only visible partsare the incisive incisure rostrally and the

6 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 295

sphenoid incisure caudally) and the ventralnasal concha. We also describe the parscochlearis of the petrosal and the middle earossicles, which is included in the NAV in theorganum vestibulocochlearis (organa sen-suum). To that, we add internal or medialviews of elements of the auditory region,namely the middle ear ossicles and thepetrosal. For this description, we usedpetrosals and middle ear ossicles of Pteropuslivingstonii, which were available detachedfrom the skull.

Using the partially disarticulated skulls ofPteropus livingstonii AMNH 274466 and274477, we describe the internal surfaces ofthe skull. Ten such surfaces are available forexamination as separate units, each includingone to several bones, depending on the stageof bone fusion in different parts of the skull.These internal surfaces are the nasal, pre-maxillary, maxillary (including the maxillaand the ventral nasal concha), palatine,fronto-ethmoid complex (including also thevomer), presphenoid (including presphenoidand orbitosphenoid), basisphenoid (includingthe regions corresponding to the basisphe-noid and alisphenoid), parietal (includingparietal and interparietal), squamosal, andoccipital (including the four occipital bones).In addition, we describe the shape of suturesthat become visible only with disarticulationof the skull elements. The internal surfaces ofthe petrosal and ectotympanic are treated inthe corresponding treatments of those bones.

For the sake of completeness, we alsodescribe in detail the hyoid apparatus and thelarynx, i.e., the posterior part of the visceralor branchial skeleton, which is frequentlypreserved together with macerated osteolog-ical material and is a potential source ofcharacters in comparative anatomy, especial-ly in Megachiroptera. We used the subadultfemale Pteropus tonganus USNM 566608 asthe subject of our description; other speci-mens (detailed below) were used to drawsome basic comparisons within Pteropus. Inour centerpiece specimen, the hyoid appara-tus is intact and detached from both the skulland the laryngeal elements. For comparisonsand further illustration, we direct the readerto Sprague (1943), who studied the hyoid andlarynx of members of each bat familyrecognized at the time, including megachir-

opterans sampled from main taxonomicgroupings based on Andersen (1912).

We used the entire sample of Pteropus lyleito describe the permanent dentition in anexhaustive way. This includes dental formula,pattern of occlusion and tooth wear, anda detailed description of the structure of eachtooth. The convention used for tooth abbre-viation is initial letter for each tooth type(i.e., incisors, canines, premolars, and mo-lars), in upper case for upper teeth and inlower case for lower teeth, followed bya number indicating the individual tooth.For instance, I2 denotes the second upperincisor, C denotes the upper canine, P4denotes the fourth upper premolar, and m3denotes the third lower molar. In dentalformulae, we give the number of teetharranged by tooth type, using upper case.The dental formula of P. lylei is I2/2, C1/1,P3/3, M2/3, indicating that the speciespossesses 2 upper/2 lower incisors, 1 upper/1lower canine, 3 upper/3 lower premolars, and2 upper/3 lower molars. Premolars aredesignated P1, P3, P4, p1, p3, and p4; thatis, P2 and p2 are assumed to be missing inbats in general. The dental formula for thedeciduous dentition is dI2/2, dC1/1, dP2/2.

The sectioned Pteropus fetus was used toreconstruct associations between soft tissuesand osteological structures. The contents offoramina are described in a separate section.Other observations (e.g., muscle attachments)are included in sections that deal with theappropriate bones. For the soft-tissue struc-tures, we use English versions of NAV terms,unless noted.

Comparisons were made between youngand adult individuals in order to describeontogenetic changes that affect cranial oste-ology. Other comparisons were made withother megachiropterans so as to evaluate thelevel of generality of descriptions of particu-lar bones or structures. Comparisons of thiskind were primarily made with other pter-opodine megachiropterans, a group that,according to Bergmans (1997), includesPteropus (67 species; Simmons, 2005), Pter-alopex (5 or 6 species), Acerodon (6 species),Neopteryx (1 species), and Styloctenium (1species). Eidolon (2 species) may join thisgroup as well (Giannini and Simmons, 2005).For selected comparisons (e.g., variation in


foramina), a wider sample of megachiropter-ans was considered.

Usage of directional terms varies; ingeneral, we follow Evans (1993) and theNAV. In most skull structures, we use rostral(or anterior) and caudal (or posterior),dorsal, and ventral. In oral and dentalstructures, we use lingual (or medial), buccal(or lateral, or vestibular), occlusal, rostral (ormental), caudal, upper, and lower. In thehyoid apparatus, we use cranial, caudal,lateral, medial, proximal, and distal. Finally,following Evans (1993), nomenclature ofjoints includes the joint types synovium,synchondrosis, and suture, the latter fallinginto four categories: plane, squamous, foliate,and serrate. Specific joints are referred to byeither their English or Latin names, exceptthe sutura squamosa (between the squamosaland parietal bones), which is always referredto in Latin to avoid confusion with the suturetype of the same English name that occurswidely in the skull.

THE SKULL AS A WHOLE

REGIONS OF THE SKULL

The rostrum is formed by the paired nasal,premaxilla, maxilla, ventral nasal concha,palatine, lacrimal, jugal, and mandible (ossafaciei). In Pteropus lylei CM 87972, therostrum, as measured from the rostralmostedge of the premaxilla to the caudalmost tipthat the palatine contributes to the ectopter-ygoid process, is slightly longer than half thelength of the entire skull. The cranium isformed by the paired frontal, parietal,pterygoid, orbitosphenoid, alisphenoid, squa-mosal, petrosal, entotympanic, ectotympanic,and exoccipital (plus the middle ear ossiclesin the auris), and the unpaired interparietal,vomer, ethmoid, presphenoid, basisphenoid,basioccipital, and supraoccipital (ossa cranii).We have examined the skull of P. lylei CM87972 and its structures in dorsal (fig. 1),lateral (fig. 2), ventral (fig. 3), rostral (fig. 4),and oblique occipital (fig. 5) views, as well asthe mandible in lateral (fig. 6), occlusal(fig. 7), and mental (fig. 8) views.

The apex (regio naris) is formed by thepremaxillae ventrolaterally and the nasalsdorsally, which enclose the osseous nasal

opening (apertura nasi ossea) or externalnasal aperture. The dorsal surface of therostrum (regio dorsalis nasi) is formed chieflyby the nasals, which are edged by thedorsalmost extension of the maxillae laterally(fig. 1). The lateral wall of the rostrum (regiomaxillaris) is formed almost in its entirety bythe rostral process of the maxilla (fig. 2). Thehard palate (palatum osseum) is composed ofthe palatine process of the maxilla rostrolat-erally and the transverse process of thepalatine caudally (figs. 3, 9). The premaxilladoes not contribute to the hard palatebecause its palatine process is not ossified.The zygomatic arch (arcus zygomaticus, regiozygomatica) or zygoma is formed by thezygomatic process of the maxilla and thesmall jugal bone, which articulate caudallywith the zygomatic process of the squamosalin the temporal region (see fig. 2 and below).The orbital region (regio orbitalis), in themiddle of the skull laterally, is a largedepression containing the fossa for theeyeball (bulbus oculi) or orbit (orbita). Ventralto the orbit is the pterygopalatine fossa (fossapterygopalatina). Dorsal to the orbit is theforehead (frons) of the frontal region (sinci-put, regio frontalis), which is formed exclu-sively by the frontal bone (fig. 1). Caudal tothe orbital region is the rostral aspect of thebraincase, with the fossa temporalis and fossainfratemporalis dorsally and ventrally, re-spectively. In the temporal region (regiotemporalis), the squamosal projects rostrolat-erally its zygomatic process, which comprisesthe posterior third of the zygomatic arch. Theroot of the zygomatic process (figs. 3, 5)overlies the glenoid fossa (fossa mandibu-laris), the cranial component of the tempo-romandibular joint (articulatio temporo-mandibularis, a synovial joint). Anothercomponent of the temporal region is theauditory region (auris), including the petrosalbone, ectotympanic, entotympanic, and themiddle ear ossicles, located ventromedial tothe squamosal and lateral to the basioccipital(see figs. 3, 5, and below). The dorsolateralaspect of the parietal region (regio parietalis,formed by the parietals and interparietal) isthe planum parietale, the largest exposure ofthe braincase. The temporal and parietalregions provide both protection to the brainand origin to the m. temporalis.


In the ventral side, caudal to the hardpalate (fig. 10), the choanae open anteriorlyinto the paired nasopharyngeal meatus (me-atus nasopharyngeus). The basicranium (basiscranii externa) forms, in tandem with theventral component of the occipital complex(see below), the floor of the braincase (fig. 3).It extends from the dorsolateral orbitosphe-noid and alisphenoid bones (alae temporaleset orbitales), which provide osseous basementto the caudal orbit and the infratemporalfossa, to the medial (pre- and basi-) sphenoidbones, which roof the nasopharyngeal mea-tus. Four ossifications—the unpaired su-praoccipital and basioccipital (dorsal andventral) and the paired exoccipitals (later-al)—as well as a small exposure of thepetrosal, form the occiput, surrounding thelarge foramen magnum for the passage of thespinal cord and associated vessels (fig. 5).

The paired mandible consists of a tooth-bearing body connected anteriorly with itsbilateral counterpart through the mandibularsymphysis, and a ramus posteriorly (figs. 6,7). The latter has a coronoid process anda mandibular condyle that articulates withthe squamosal, forming the mandibularcomponent of the temporomandibular joint.

ROSTRAL VIEW OF THE SKULL

The apex of the rostrum consists of a large,almost heart-shaped external nasal aperturebordered ventrolaterally by the dorsally di-vergent premaxillae and dorsally by thenasals. Visible through the external nasalaperture inside the nasal cavity (cavum nasi)are the paired ventral nasal concha (conchanasalis ventralis) or maxilloturbinate, theincisive incisure of the vomer (also visiblethrough the incisive fissure ventrally), thenasal septum (septum nasi osseum), and thevery tip of the ethmoturbinals (ethmoturbi-nalia). Four incisors are attached to thepremaxillae (see Dentition below).

DORSAL SURFACE OF THE SKULL

The principal components of the rostrumare the dorsal surface of the nasals mediallyand the rostral process of the maxillaelaterally, with a limited contribution of thepremaxillae in the rostrolateral angles. The

breadth of the rostrum increases abruptly atthe level of the canines to accommodate thecanine roots and the correspondingly promi-nent juga. There is only a modest widening ofthe rostrum caudal to the canines. Thelacrimal is visible laterally in dorsal view(fig. 1). On the ventrocaudal angle of therostrum, the large root of the zygomatic arch,in association with the alveolar process of themaxilla, forms a roughly triangular plate.The rostrolateral edge of the zygomatic rootis a bridge of bone perforated by theinfraorbital canal (canalis infraorbitalis).The horizontal plate of the root, widelyvisible in dorsal view, represents the maxil-lary tuberosity. The open roots of M1 andM2 protrude in that surface—which is also thefloor of the pterygopalatine fossa, a space thatfunnels rostrally into the infraorbital canal.The caudal edge of the zygomatic root isdeeply concave (fig. 3); it converges caudolat-erally with the rostrolateral edge of the root,leading to the laterally compressed archesthemselves. Shortly after, the maxillary part ofthe arch meets the small jugal, which consti-tutes the middle portion of the arch. Theposterior zygomatic root, dorsoventrally com-pressed, is contributed by the zygomaticprocess of the squamosal, which joins thebraincase laterally. The posterior zygomaticroot projects rostrolaterally from the brain-case and widely overlaps the jugal dorsally.

The frontal forms the central portion of thedorsal surface of the skull (fig. 1). The dorsalaspect of the frontal may be divided intoa short, preorbital area, a laterally biconcaveinterorbital area rostrally, bounded by thesupraorbital margin (margo supraorbitalis),and an approximately rectangular postorbitalplate caudally. The prominent postorbitalprocesses (processus zygomaticus) arise be-tween the two posterior areas. The largepostorbital foramen pierces the root of eachpostorbital process.

The braincase is large and bulbous, witha roughly piriform shape. CM 87872 showsa smooth cranial surface with no temporallines. The rounded surface of each parietal(planum parietale) and the interparietal cau-domedially are visible in dorsal view, whereasthe lateral contribution from the squamosalto the braincase (the squama) is hidden in thisview.


Fig. 1. Dorsal view of the skull of Pteropus lylei CM 82972, with accompanying line drawing. Scale 5

5 mm. Abbreviations: C upper canine; fr frontal; ip interparietal; ju jugal; lac lacrimal; mx maxilla; na


Fig. 1. Continued.

nasal; P3 third upper premolar; P4 fourth upper premolar; pa parietal; pal palatine; pmx premaxilla; pofpostorbital foramen; pop postorbital process; rM1 roots of first upper molar; rM2 roots of second uppermolar; sc sutura coronalis; sfl sutura frontolacrimalis; sfm sutura frontomaxillaris; sfn sutura frontonasalis;sin sutura internasalis; smi sutura maxilloincisiva; snm sutura nasomaxillaris; so supraoccipital; sopa suturaoccipitoparietalis; spip sutura parietointerparietalis; sq squamosal; ss sutura sagittalis; stz suturatemporozygomatica; szmx sutura zygomaticomaxillaris.


Fig. 2. Lateral view of the skull of Pteropus lylei CM 82972, with accompanying line drawing. Scale 5

5 mm. Abbreviations: as alisphenoid; bo basioccipital; C upper canine; ec ectotympanic; ef ethmoidalforamen; eo exoccipital; fr frontal; frt foramina for rami temporales; hf hypoglossal foramen; I1 first upperincisor; I2 second upper incisor; iof infraorbital foramen; ip interparietal; ju jugal; lac lacrimal; lacf lacrimalforamen; M1 first upper molar; M2 second upper molar; me mastoid exposure of petrosal; mx maxilla; nanasal; oc occipital condyle; os orbitosphenoid; P1 first upper premolar; P3 third upper premolar; P4 fourthupper premolar; pa parietal; pal palatine; pcp paracondylar process; pmx premaxilla; pof postorbitalforamen; pop postorbital process; pt pterygoid; ptpfi pterygopalatine fissure; rpm rostral process ofmalleus; sc sutura coronalis; sfm sutura frontomaxillaris; smi sutura maxilloincisiva; so supraoccipital;soipa sutura occipitointerparietalis; sopa sutura occipitoparietalis; soipa sutura occipitointerparietalis; spfsphenopalatine foramen; spip sutura parietointerparietalis; spof sphenorbital fissure; sq squamosal; sspalsutura sphenopalatina; sspar sutura sphenoparietalis; ssq sutura squamosa; zpmx zygomatic process ofmaxilla; zpsq zygomatic process of squamosal.


LATERAL SURFACE OF THE SKULL

The rostrum is formed chiefly by themaxilla in lateral view (fig. 2), and its gentlyconvex lateral surface is marked anteriorly bythe alveolar juga of the canines. Rostrally,the procumbent premaxilla projects anterior-ly beyond the rostral end of the nasal;ventrally, it extends below the level of thealveolar line. The alveolar line is sinuous,with rounded valleys and peaks correspond-ing to the locations of individual teeth andspaces between them. The upper tooth rowconsists of two incisors followed by a largecanine, a minute P1 and four well-developedcheek teeth (two premolars and two molars;see Maxilla and Dentition). Dorsally, therostrum gently ascends to meet the frontal,which in turn continues rising to the coronal(5 frontoparietal) suture (seen in dorsalview). Posteriorly, the thin, elongated anteri-or zygomatic root projects caudolaterallyfrom the maxilla. The anterior zygomaticroot is pierced by a large infraorbital canal.The anterior zygomatic root meets the jugalwell away from the contact with the alveolarprocess of the maxilla. The jugal occupies themiddle portion of the dorsoventrally thin,gently arched, mediolaterally compressedzygomatic arch, and it is widely overlaid bythe zygomatic process of the squamosal.

The orbit is large, placed slightly off centerin the middle portion of the skull (fig. 2). Therounded orbital outline is delimited rostro-ventrally by the small, triangular lacrimaland the anterior root of the zygomatic arch,and dorsally by the frontal and its postorbitalprocess. The orbit is not bounded caudally bybone as in individuals of some large-sizedspecies of Pteropus and allies (Acerodon,Pteralopex), in which the orbital ligament(lig. orbitale) ossifies to produce a completeosseous bar connecting the postorbital pro-cess and zygomatic arch (this bar is some-times called the jugal spine). The orbital fossais gently concave and is continuous caudallywith the temporal fossa.

Ventral to the orbit is the pterygopalatinefossa, which is formed mainly by the oblique,mediodorsally oriented plane of the perpen-dicular process of the palatine. There is onlya faint infratemporal crest on the alisphenoiddelimiting the temporal fossa from the

infratemporal fossa in CM 87972. In oursample, some specimens (e.g., AMNH237593) show a slightly more robust infra-temporal crest. In the ventrocaudal conjunc-tion of the orbit and pterygopalatine fossaare the openings of the optic canal andsphenorbital fissure, as well as the transversecleft that separates the palatine and thepterygoid, the pterygopalatine fissure (fig. 2).Caudal to the sphenorbital fissure, theconvex alisphenoid forms the rostroventralborder of the braincase. Caudal to thatarea is the glenoid fossa, barely visible inlateral view, underlying the posterior zygo-matic root. Immediately caudal to theglenoid fossa, the external acoustic meatus(meatus acusticus externus) opens laterally,showing an arched dorsal margin that is theattachment area of the small, oval ectotym-panic. The manubrium of the malleus isvisible inside the ectotympanic. Where thetemporal area merges with the occipitalregion, three successively larger protuber-ances appear caudally: the posttympanicprocess of the squamosal, the paracondylarprocess of the exoccipital, and the occipitalcondyle.

In lateral view (fig. 2), the braincase asa whole is oval in shape, with the mostconvex point approximately at the center ofthe parietal. The braincase shows two dis-tinctive traits. First, the ventral deflection ofthe basicranial axis with respect to the rostralaxis is extraordinarily pronounced, which isall the more noticeable if the rostral axis isheld horizontally. If an imaginary line isprojected caudally at the level of the alveolarline, it intersects a point on the cranium atthe level of the external occipital protuber-ance of the supraoccipital. Second, theoccipital region protrudes caudally, formingthe so-called ‘‘tubular occiput’’ (Miller, 1907;Andersen, 1912) typical of adult pteropodinemegachiropterans (especially Pteropus). Inhis description of the skull, Andersen (1912:61) stated that the ‘‘occiput [is] producedbackward and downward, as a short tube’’.This trait is more easily observed if the skullis held with the basicranial axis alignedhorizontally. In that position, the occipitalcondyles project caudally beyond an imagi-nary vertical line at the level of the incipientnuchal crest.


Fig. 3. Ventral view of the skull of Pteropus lylei CM 82972, with accompanying line drawing. Scale 5

5 mm. Abbreviations: apf accessory palatine foramen; as alisphenoid; bcc posterior basicochlearcommissure; bcf basicochlear fissure; bo basioccipital; bs basisphenoid; C upper canine; cf carotidforamen; ec ectotympanic; ecptp ectopterygoid process; en rostral entotympanic; eo exoccipital; fc fenestracochleae; if incisive fissure; fm foramen magnum; fo foramen ovale; fr frontal; gf glenoid fossa; hamhamulus pterygoideus; hf hypoglossal foramen; I1 first upper incisor; I2 second upper incisor; jf jugularforamen; ju jugal; M1 first upper molar; M2 second upper molar; mapf major palatine foramen; me


Fig. 3. Continued.

mastoid exposure of petrosal; mpf minor palatine foramen; mx maxilla; oc occipital condyle; P1 first upperpremolar; P3 third upper premolar; P4 fourth upper premolar; pa parietal; pal palatine; pgf postglenoidforamen; pif piriform fenestra; pmx premaxilla; pop postorbital process; pr promontorium of petrosal; pspresphenoid; pt pterygoid; ptp posttympanic process; rpm rostral process of malleus; simx suturaintermaxillaris; sipal sutura interpalatina; sisp synchondrosis intersphenoidalis; smi sutura maxilloincisiva;so supraoccipital; spamx sutura palatomaxillaris; sq squamosal; sspo synchondrosis sphenoccipitalis; stzsutura temporozygomatica; szmx sutura zygomaticomaxillaris; vnc ventral nasal concha or maxilloturbinal.


VENTRAL SURFACE OF THE SKULL

The ventral surface of the skull shows thehard palate (figs. 3, 9), the basipharyngealcanal or choanal region (figs. 3, 10), thebasicranium, the auditory region, and theventral side of the zygomatic arches (fig. 3).The premaxillae project beyond the rostraledge of the canines. A wide I2–C diastema ispresent. The C–C distance is markedly widerthan the maximum premaxillary width. Thebulk of the rostrum ends abruptly in front of

the canines. Rostral to the C–C line is thelarge incisive fissure surrounded rostrolater-ally by the left and right premaxillae, whichproject and converge to each other rostrome-dially. The length of the hard palate(23.8 mm, measured from the rostralmostend of the palatine process of the maxilla tothe caudalmost extension of the palatine inthe midsagittal line) is considerably greaterthan its width (15.2 mm, measured as thedistance between the lateralmost points of theleft and right M1). The upper tooth row is

Fig. 4. Pteropus lylei AMNH 237595, rostral view of the skull. Scale 5 5 mm. Abbreviations: C uppercanine; ccr conchal crest; fr frontal; gc groove of upper canine; I1 first upper incisor; I2 second upperincisor; ioc infraorbital canal; lac lacrimal; na nasal; nas nasal septum; pmx premaxilla; pop postorbitalprocess; v vomer; vnc ventral nasal concha; zpmx zygomatic process of maxilla.


only slightly divergent from the canine rootto M2. The interdental palate is a smooth,gently concave surface perforated laterally byforamina of the palatine nerve and vesselscomplex (see Maxilla, Palatine, and Foram-ina Contents and Homology). There isa large, caudally projecting postdental palate.Laterally, the postdental palate is roughlystraight, converging only slightly mediallyuntil it reaches the pterygoid, where thepalate contributes to the large ectopterygoidprocess. Medially, the postdental palate takesthe shape of a wide >, ending in the midpointbetween the caudal border of M2 and theectopterygoid process. This caudal edge isslightly deflected ventrally, increasing theconcavity of the postdental palate. Immedi-ately caudal is the ventrally open basiphar-yngeal canal, which is roofed by the pre-sphenoid and basisphenoid and framedlaterally by the pterygoids (fig. 10). In thisarea, the nasopharyngeal duct is wide andrelatively shallow. Lateral to the pterygoid isthe convex surface of the alisphenoid, whichis pierced by the large foramen ovale. Lateralto the foramen ovale is the large glenoid fossaand the posterior root of the zygomatic arch.

The basioccipital presents a wide, slightlyconvex surface that leads caudally to thelarge opening of the foramen magnum andthe projecting occipital condyles. Laterally,the basioccipital has a relatively narrowcontact with the petrosal in the posteriorbasicochlear commissure. Rostral to thiscommissure is the basicochlear fissure, whichon the left side of CM 87972 is confluent withthe piriform fenestra, whereas on the rightside it is separated from the latter by thesmall entotympanic (see details in Basiocci-pital). The entotympanic element is a short,peglike rostral entotympanic, preserved onlyon the right side in CM 87972 and variouslyattached to the basicranium in other speci-mens (see Entotympanic). Caudal to the

Fig. 5. Pteropus lylei CM 82972, obliqueoccipital view. Scale 5 5 mm. Abbreviations: asalisphenoid; bcc posterior basicochlear commis-sure; bcf basicochlear fissure; bo basioccipital; bsbasisphenoid; cppt caudal process of pterygoid;ctpp caudal tympanic process of petrosal; ecectotympanic; ecptp ectopterygoid process; enrostral entotympanic; eo exoccipital; fc fenestracochleae; fm foramen magnum; fo foramen ovale;gf glenoid fossa; ham hamulus pterygoideus; hfhypoglossal foramen; hppal horizontal process ofpalatine; ip interparietal; jf jugular foramen; mamalleus; me mastoid exposure of petrosal; mfmastoid foramen; oc occipital condyle; os orbito-sphenoid; pa parietal; pcp paracondylar process;pgf postglenoid foramen; pif piriform fenestra;pppal perpendicular process of palatine; pr pro-

rmontorium of petrosal; ps presphenoid; pt ptery-goid; ptp posttympanic process; ptpfi pterygopala-tine fissure; rmppt rostromedial process of ptery-goid; rpm rostral process of malleus; siocblsynchondrosis intraoccipitalis basilateralis; so su-praoccipital; sq squamosal; zpsq zygomatic processof squamosal.


posterior basicochlear commissure is thelarge jugular foramen. Caudal to this fora-men is the paracondylar process of theexoccipital.

The petrosal lies lateral to the basioc-cipital. It has a rounded promontoriumwith a large, caudoventrally directedround window, a large fossa for the m.stapedius caudolaterally, and a large, ratherfeatureless mastoid exposure caudally. Theectotympanic attaches to the border ofthe external acoustic meatus (of whichthe posttympanic process is visible ventral-ly). The ectotympanic is inclined ventrome-dially. The anterior or rostral process ofthe malleus is visible on the anterior sur-

face of the ectotympanic ring, with theglenoid fossa in the background. The largepostglenoid foramen appears between theglenoid fossa and the external acousticmeatus.

CAUDAL SURFACE OF THE SKULL

The occiput (fig. 5) is dominated by thevery large foramen magnum. The occipitalcondyles, the cranial counterparts of theatlanto-occipital joint (articulatio atlanto-occipitalis), are obliquely placed on thelateral (and slightly ventral) margin of theforamen. Flanking the condyles are thesmall, ventrally oriented paracondylar

Fig. 6. Pteropus lylei CM 82972, lateral view of the left mandible, with accompanying line drawing.Scale 5 5 mm. Abbreviations: amf anterior mental foramen; an angle of mandible; c lower canine; conmandibular condyle; cor coronoid process of mandible; i1 first lower incisor; i2 second lower incisor; m1first lower molar; m2 second lower molar; m3 third lower molar; ms mental surface; p1 first lowerpremolar; p3 third lower premolar; p4 fourth lower premolar; pmf posterior mental foramen.


Fig. 7. Pteropus lylei CM 82972, occlusal view of the mandible, with accompanying line drawing. Scale5 5 mm. Abbreviations: c lower canine; con mandibular condyle; cor coronoid process of mandible; i1 firstlower incisor; i2 second lower incisor; m1 first lower molar; m2 second lower molar; m3 third lower molar;mas mandibular symphysis; p1 first lower premolar; p3 third lower premolar; p4 fourth lower premolar.


processes of the exoccipital and, lateral tothem, the flat mastoid exposure of thepetrosal. The tubular structure of the occiputis evinced, in this view, by the pronouncedslope of the supraoccipital area. In adultPteropus lylei (e.g., AMNH 237593), a strongnuchal crest (crista nuchalis) is present (seeOccipital Complex and Comparisons).

THE SKULL BONES

ROSTRAL BONES (OSSA FACIEI)

NASAL

The nasal (os nasale) is a paired bone thatcovers the dorsum of the rostrum from itsapex to the level of P4 (fig. 1). The nasalshave their rostral margin free (fig. 2), andarticulate with each other in the medianplane, forming the straight internasal suture(sutura internasalis; fig. 1). In turn, each nasalcontacts the premaxilla anteroventrally,forming the nasoincisive suture (sutura na-soincisiva), the maxilla lateroventrally, form-ing the nasomaxillary suture (sutura naso-maxillaris), and the frontal caudally, formingthe frontonasal suture (sutura frontonasalis).

The dorsal surface of the nasals is roughlyflat, with the rostrolateral angle slightlydeflected downward (figs. 1, 2). The rostraledge is roughly square and forms the dorsaledge of the external nasal aperture, with littlenasal overhang of that aperture. The naso-maxillary suture is gently bowed inward andruns along most of the length of the nasals.The frontonasal suture is W-shaped due tothe roughly triangular posterolateral frontalprocess (processus frontalis) of each nasalpenetrating the frontal as a wedge (fig. 1).Laterally, only the anterior tip of the nasals isvisible (fig. 2). There are no foramina in thenasals.

PREMAXILLA

The premaxilla (os incisivum) is a pairedbone located in the apex of the skull, formingthe ventrolateral rim of the external nasalaperture (figs. 1–4). In the Pteropodidae, thepremaxilla is composed of a lateromediallyoriented body (corpus ossis incisivi), some-times called the alveolar process of thepremaxilla, and the dorsoventrally orientednasal process (processus nasalis), whereas thepalatine process (processus palatinus) is notossified. The left and right bodies articulateby a plane suture, the short interincisivesuture (sutura interincisiva). Each body bearsthe alveoli for two incisors (in general, alveolidentales). The depth of the body increasesfrom the alveolus of I1 to I2, and the alveolarline (margo alveolaris of the premaxilla)gently arches above each tooth.

The nasal process is a laterally compressedlamina that reaches the nasal dorsally,forming the nasoincisive suture, and contactsthe rostral process of the maxilla caudally,forming the foliate maxilloincisive suture(sutura maxilloincisiva; equivalent to suturaincisivomaxillaris of the dog). In lateral view,the nasal process shows as a bar of bonedirected dorsocaudally, maintaining a roughlyconstant width throughout its length. Inrostral view, the two nasal processes diverge

Fig. 8. Pteropus lylei AMNH 237595, rostralview of the mandible. Scale 5 5 mm. Abbrevia-tions: amf anterior mental foramen; c canine; jadental juga; i1 first upper incisor; i2 secondupper incisor.

R

Fig. 9. Pteropus lylei CM 82972, ventral view of hard palate. Scale 5 5 mm. Abbreviations: apfaccessory palatine foramina; bs basisphenoid; C upper canine; ecptp ectopterygoid process; hppalhorizontal process of palatine; I1 first upper incisor; I2 second upper incisor; if incisive fissure; iiv incisura

ROSTRAL BONES (OSSA FACIEI)


incisiva of vomer; M1 first upper molar; M2 second upper molar; mapf major palatine foramina; mpfminor palatine foramina; mx maxilla; P1 first upper premolar; P3 third upper premolar; P4 fourth upperpremolar; palp palatine process of maxilla; pmx premaxilla; ps presphenoid; pt pterygoid; ptc opening ofpterygoid canal; ptpfi pterygopalatine fissure; sisp synchondrosis intersphenoidalis; vnc ventralnasal concha.


dorsally, forming a V-shaped structure, withthe nasals dorsally bridging the gap betweenthe two arms of the V, thereby closing theperimeter of the external nasal aperture. Thenasoincisive suture is plane and gentlyconvex. The maxilloincisive suture is incom-plete dorsoventrally, so there is a notchseparating the ventral half of the premaxillaand the maxilla. As a consequence of thisnotch, the premaxillary bodies do not artic-ulate with the maxilla, creating a wide di-astema between I2 and C.

In ventral view (figs. 3, 9), the left and rightpremaxillae surround a single large medianopening between themselves and the anterioredge of the palatine process of the maxilla.This opening, the incisive fissure (the doublefissura palatina of the dog), is formed by thecoalescence of the paired incisive foramina(see Foramina below). There are no other

foramina in the external surface of thepremaxillae.

MAXILLA

The maxilla (os maxillare) is paired and isthe major component of the rostrum, togeth-er with the premaxilla forming the upper jaw.Each maxilla consists of a body with a largeexternal surface or rostral process (faciesfacialis), which constitutes the bulk of thelateral wall of the rostrum, and a palatineprocess (processus palatinus), which forms theanterior portion of the hard palate (palatumosseum). At the intersection of these twoprocesses is the alveolar surface (processusalveolaris), which bears the alveoli for sixteeth and contributes to the anterior floor ofthe orbit caudally (figs. 2, 3, 9). The twomaxillae articulate with each other along the

Fig. 10. Pteropus lylei CM 82972, ventral view of the nasopharyngeal region. Scale 5 5 mm. Indicatedon the right ectopterygoid process are the contributions of its three component bones: the palatine (pal),alisphenoid (as), and pterygoid (pt). Abbreviations: app apex parties petrosa; as alisphenoid (contributionof the alisphenoid to the ectopterygoid process); bcf basicochlear fissure; bo basioccipital; bs basisphenoid;cf carotid foramen; cppt caudal process of pterygoid; ec ectotympanic; ecptp ectopterygoid process; enrostral entotympanic; fo foramen ovale; gf glenoid fossa; ham hamulus pterygoideus; hppal horizontalprocess of palatine; isv incisura sphenoidalis of vomer; ju jugal; lppt lateral process of pterygoid; osorbitosphenoid; pal palatine (contribution of the palatine to the ectopterygoid process); pgf postglenoidforamen; pif piriform fenestra; pop postorbital process; pppal perpendicular process of palatine; pspresphenoid; pt pterygoid (contribution of the pterygoid to the ectopterygoid process); ptc pterygoid canal;ptpfi pterygopalatine fissure; rmppt rostromedial process of pterygoid; rpm rostral process of malleus; sispsynchondrosis intersphenoidalis; spc sphenoidal crest; sq squamosal; sspo spheno-occipital synchondrosis.


midsagittal line in the anterior hard palate,forming the intermaxillary suture (suturaintermaxillaris, part of sutura palatina med-iana in the NAV).

The rostral process of the maxilla contactsthe premaxilla anteriorly, the nasal dorsally(sutures described above), the frontal poster-odorsally, forming the frontomaxillary suture(sutura frontomaxillaris), the lacrimal poster-iorly in the orbital margin (margo orbitalis),forming the lacrimomaxillary suture (suturalacrimomaxillaris), and the jugal posteroven-trally, forming the zygomaticomaxillary su-ture (sutura zygomaticomaxillaris). Inside thepterygopalatine fossa (fossa pterygopalatina)ventral to the orbit, the maxilla contacts the

lacrimal dorsally and the perpendicularlamina of the palatine posteriorly, the latterforming the palatomaxillary suture (suturapalatomaxillaris in Evans, 1993; sutura pala-tina transversa in the NAV). Finally, theventral limit of the rostral process in lateralview is the sinuous alveolar line (margoalveolaris of the maxilla).

The surfaces of the rostral processes arealtered by the prominent juga of the canines,whose roots are located high on the side ofthe nasomaxillary suture. The roots of thepostcanine teeth are clearly visible throughthe bone but do not significantly modify therostral surface (i.e., the tooth roots do notalter the surface to form alveolar juga).

Fig. 11. Pteropus lylei CM 87972, ventrolateral view of the right orbital region. Scale 5 5 mm.Abbreviations: as alisphenoid; bo basioccipital; ec ectotympanic; ef ethmoidal foramen; fdv foramen forfrontal diploic vein; fo foramen ovale; fofr facies orbitalis of frontal; frt foramen for ramus temporalis; gfglenoid fossa; ham hamulus pterygoideus; hf hypoglossal foramen; ioc infraorbital canal; jf jugularforamen; ju jugal; lac lacrimal; M1 first upper molar; ma malleus; me mastoid exposure; mpf minorpalatine foramen; mx maxilla; oc occipital condyle; opc optic canal; os orbitosphenoid; pa parietal; pcpparacondylar process; pgf postglenoid foramen; pop postorbital process; pppal perpendicular process ofpalatine; ptmx pterygoid process of maxilla; ptp posttympanic process; rpm rostral process of malleus; scsutura coronalis; siobl synchondrosis intraoccipitalis basilateralis; so supraoccipital; spof sphenorbitalfissure; sqa squama of squamosal; ssq sutura squamosa; zpmx zygomatic process of maxilla; zpsqzygomatic process of squamosal.


Dorsal to the P4–M1 embrasure (in general,septa interalveolaria) and between the poste-rior root of P4 and the orbital rim, the rostralprocess is pierced by the infraorbital foramen

(foramen infraorbitale), the anterior openingof the infraorbital canal. This foramen iselliptical in shape with its major axis orientedat ca. 45 degrees to the alveolar line. Insidethe left infraorbital canal, a foramen in thefloor represents the alveolar canal (canalisalveolaris) for the rostral and middle superioralveolar nerves. Apparently, the same fora-men is also present on the right side but isdisplaced slightly posteriorly into the orbitright behind the ventral margin of themaxillary foramen (foramen maxillare), thecaudal opening of the infraorbital canal(fig. 12). No other foramina are present inthe rostral process, but traces of a fewnutrient foramina (now obliterated) areirregularly distributed on the rostralsurface.

The posterior edge of the rostral processdescribes an oblique line that successivelycontacts the frontal and the lacrimal, formsthe ventral portion of the orbital rim,and continues in the zygomatic arch poster-iorly (fig. 2). The frontomaxillary suture isroughly straight and is minutely serrated,running posterolaterally from the external-most point of nasal–frontal contact to thelacrimal (this area is the frontal process ofthe maxilla or processus frontalis of thedog). The lacrimomaxillary suture is concave.Ventral to this, the maxilla forms the infra-orbital margin (margo infraorbitalis). Poster-oventrally, a flat lamina of bone bridgesover the short infraorbital canal and con-tinues backward to form the elongatedzygomatic process of the maxilla (processuszygomaticus), which contacts the jugal atapproximately the midpoint of the ventralorbital semicircumference. Therefore, theanterior zygomatic root lies entirely in themaxilla.

The zygomatic process is slender, with aninconspicuous ventral crest in the massetericmargin (margo massetericus of the maxilla)extending from the alveolar line (at the levelof the anterior half of M1) to the contactwith the jugal. This crest is for the origin ofthe m. masseter. The foliate zygomaticomax-illary suture is very irregular, concave later-ally, and sinuous medially. Laterally, thezygomatic process rises slightly posteriorly,so the articulation with the jugal is above (ca.1 mm) the alveolar line. The root of the

Fig. 12. Pteropus lylei CM 82972, caudolateralview of the right orbital region. Scale 5 5 mm.Abbreviations: ac alveolar canal; apf accessorypalatine foramina; C upper canine; fr frontal; iocinfraorbital canal; ju jugal; lac lacrimal; lacflacrimal foramen; lacfe lacrimal fenestra; mpfminor palatine foramen; mx maxilla; mxtu maxil-lary tuberosity; P3 third upper premolar; P4fourth upper premolar; pa parietal; pal palatine;pc palatine canal; pop postorbital process; r1M1anterior root of first upper molar; r2M1 posteriorroot of first upper molar; rM2 roots of secondupper molar; spf sphenopalatine foramen; vflacvascular foramen of lacrimal.


zygomatic process is horizontally expandedas a flat, roughly triangular plate and joinsthe rear of the alveolar surface medially inthe anterior orbital floor (figs. 1, 3).

The alveolar surface is in the ventrolateralportion of the maxilla. It contains the alveolifor the canine and five postcanine teeth: threepremolars (P1, P3, and P4) and two molars(M1 and M2). The caudal portion of thealveolar surface of the maxilla contributes tothe anterior orbital floor. In lateral view, thealveolar border (margo alveolaris) describesa low, gentle sinusoid with small roundedpeaks in the P1–P3, P3–P4, and (shallower)P4–M1 embrasures, and small roundedvalleys in P3 and P4 between the two rootsof each tooth. Behind the P4–M1 embrasure,the alveolar border is relatively smooth andstraight. The alveolus for the canine is thelargest one, oval in shape, with its edge thinand sharply defined laterally and less somedially. Posteriorly, the canine alveolus ispartially coalesced with the extremely smallalveolus of the minute P1. There are nomarked diastemata. The alveoli of P3 and P4are similar in size and shape; the M1 alveolusis slightly longer than the P3 or P4 alveoli;the alveolus of M2 is half the length of theM1 alveolus but approximately the samewidth anteriorly, decreasing slightly poster-iorly. Ventrally, the posterior edge of thealveolar area follows the outline of M2 andtapers to a small point. This is the pterygoidprocess of the maxilla (processus pterygoi-deus; fig. 11), which is a free projection in thedog. In Pteropus, the pterygoid process abutsmedially the lateral edge of the palatine bone,and there is no free-standing portion. Withinthe pterygopalatine fossa, the surface of theposteriorly directed alveolar process is swol-len between the shelf of the zygomatic rootand the sphenoidal process of the palatine,forming the maxillary tuberosity (tuber max-illae; fig. 12). The two open roots of M1 arevisible anteriorly in the orbital floor throughtheir respective alveolar foramina (foraminaalveolaria), the anterior one partially con-cealed by bone, as well as the two smaller(also open) roots of M2 posteriorly. On bothsides, the M2 roots are displaced mediallyfrom the line of the M1 roots, the latterseemingly in line with the roots of the othercheek teeth. The rostrally directed alveolar

canal, which has an intramaxillary course(see below), opens immediately dorsal androstral to the anterior root of M1. Lateral tothe M1 roots lies a large, posteriorly directed,oval opening, the maxillary foramen. Thesurface of the small portion of maxillarybone immediately dorsal to the anterior rootof M1 and the maxillary foramen (i.e., themaxillary portion that contacts the lacrimalin the orbital surface) is porous and showsmany minute foramina distributed irregular-ly, in addition to one slightly larger anddistinct foramen present on both sides. At thejuncture of the lacrimal, palatine, and max-illa, there is a small vacuity of comparablesize and shape on both sides (also presentbilaterally in CM 87973), the lacrimal fenes-tra (fig. 12).

The palatine processes form a transverseshelf of bone that occupies the anterior two-thirds of the hard palate. The free, anterioredge of the maxillary halves is biconcave,each side with a small median point thatunderlies the vomer’s incisive incisure. Theintermaxillary suture is slightly raised, form-ing a low crest that extends from the anterioredge of the canine to the P4–M1 embrasure.Posteriorly, the palatine processes articulatewith the paired palatine bones, forming thepalatal portion of the palatomaxillary suture(sutura palatomaxillaris). This suture of bothmaxillary halves with their respective palatinehalves has the shape of a high arch orparabola whose vertex is in the midsagittalline at the level of the P4–M1 embrasure.However, the area of the vertex is veryirregular and slightly convex. The palato-maxillary suture terminates immediately be-hind M2. The surface of the palatine processis slightly vaulted toward the midline; thisfeature increases gently posteriorly andcontinues smoothly onto the palatinebones. The major palatine foramen (foramenpalatinus major) is located on the suturebetween the maxilla and the palatine (rightside) or immediately anterior to that suture(left side). On both sides, a palatine sulcus(sulcus palatinus) extends forward from themajor palatine foramen, converging near themidsagittal line and waning until it disap-pears at the level of P3. There are no otherforamina in the palatine process of themaxilla.


VENTRAL NASAL CONCHA

The ventral nasal concha (concha nasalisventralis), or maxilloturbinate, is a pairedbone of the nasal cavity (see Internal Surfacesof the Skull). Only its rostral end is visibleexternally, through the external nasal aper-ture (figs. 3, 4, 9). In rostral view, the rightventral nasal concha of CM 87972 hasa laterally compressed S-shape, with theconcavity of a dorsal scroll facing medially,the concavity of a ventral scroll facinglaterally, and a barely visible basal laminathat attaches laterally to the conchal crest ofthe internal surface (facies nasalis) of themaxilla. In CM 87972 the left side is similarto the right side, but the dorsal concavity isslightly smaller. In rostral oblique view, therostral end is somewhat wedge-shaped. Thespaces in the nasal cavity include therelatively wide common nasal meatus (meatusnasi communis) between the two ventral nasalconchae in front of the nasal septum, themiddle dorsal meatus (meatus nasi medius)between the dorsal aspect of the conchae andthe nasals, and the ventral nasal meatus(meatus nasi ventralis) between the ventralaspect of the conchae and the nasal surface ofthe maxilla. The rostral end of the ethmo-turbinals (ethmoturbinalia) and the nasalseptum are also visible through the externalnasal aperture (fig. 4), but the surfacesavailable for external examination are ex-tremely small (see Internal Surfaces of theSkull).

PALATINE

The palatine bone (os palatinum) is pairedand forms the caudal part of the hard palate,the lateroventral wall of the nasopharyngealmeatus, and its external counterpart, themedial wall of the pterygopalatine fossa(figs. 9–12). Each palatine has two thinlaminae: the horizontal process (lamina hor-izontalis) and the perpendicular process(lamina perpendicularis). The left and righthorizontal processes articulate along themidsagittal line in the posterior hardpalate, forming the interpalatine suture (partof sutura palatina mediana in the NAV),which is continuous with the intermaxillarysuture.

The horizontal process of the palatinerostrally contacts the palatine process of themaxilla (suture described above) and dorsallycontacts the sphenoidal incisure of thevomer, forming the vomeropalatine suture(sutura vomeropalatina dorsalis). The anteriormargin of the two palatines (at the transversesuture) is very irregularly concave. Thelateral edge is bowed outward. The caudaledge is free and deeply concave, forminga wide >-shaped margin. The lateral marginsof the postdental palate are slightly bowedinward and converge slightly toward themidsagittal line; in some specimens, a shallownotch is present in the midpoint alongsidethis margin (e.g., CM 87973). The lateral andcaudal edges meet at a caudal point thatcontacts the pterygoid (see below). Theventral surface is arched, continuing smooth-ly and accentuating the trend seen in thepalatine process of the maxilla. The inter-palatine suture is straight and plane. Thebone density of the palatine surface (faciespalatina) varies in relation to the proximity ofthe interpalatine suture and caudal palatinemargin, where the bone is noticeably thicker.In the remainder of the palatine surface, thebone is translucently thin. A series of fivesmall lateral foramina, aligned with thelateral margin of the palatine, are found nearthe lateral margin of the palatine surface. Thehomologies of these foramina are discussedat length below on the basis of the sectionedfetus (see Foramina Contents and Homolo-gy). Based on the fetus, the rostral three ofthe lateral foramina are dependents of theoverlying palatine canal (canalis palatinus)for the major palatine nerve and artery,which exit rostrally via the major palatineforamen; these three lateral foramina areidentified here as accessory palatine foramina(fig. 9). The caudal two foramina aredependents of another, larger foramen thatopens medially on the ventral surface of thepalate between the level of the third andfourth lateral foramina, identified as theminor palatine foramen (foramen palatinumcaudale). The bilateral discrepancy includesan extra medial foramen on the right side, thedouble-opening condition of the left fifthlateral foramen, and the location of the firstaccessory foramen (on the palatomaxillarysuture on the right side, on the palatine


surface on the left side). There is also a minutenutrient foramen on each side of the inter-palatine suture, located in slightly differentpositions (left side foramen is more caudal;both foramina are placed at the level of thecaudal edge of M2). The palatine surface isimpressed by a wide sulcus of conical shapethat expands medially and whose vertex is atthe minor palatine foramen.

The dorsal surface of the palate (faciesnasalis) is flat with a bilateral low ridge, thenasal crest (crista nasalis), alongside theinterpalatine suture. The sphenoidal incisureof the vomer (see below) articulates with thiscrest in the vomeropalatine suture.

The perpendicular process of the palatineexternally forms the side of the pterygopala-tine fossa (fig. 11) and internally forms thelateral wall of the nasopharyngeal meatus(fig. 10). It is oriented dorsomedially at ca. 45degrees, with a slightly arched surface. Itcontacts the maxilla rostrally (sutures de-scribed above), the frontal dorsally, formingthe frontopalatine suture (sutura frontopala-tina), the lacrimal anterodorsally, formingthe palatolacrimal suture (sutura palatolacri-malis), the presphenoid dorsomedially, form-ing the sphenopalatine suture (sutura spheno-palatina), and the pterygoid caudally,forming the pterygopalatine suture (suturapterygopalatina). A vacuity separates thecaudomedial edge of the palatine from therostromedial edge of the pterygoid, termedhere the pterygopalatine fissure (fig. 9). Thefrontopalatine suture is squamous, nearlyhorizontal, and somewhat irregular. Thepalatolacrimal suture is a short (ca. 1 mm),oblique contact on the left side, and a pointcontact on the right side. The ellipticalsphenopalatine foramen (foramen sphenopa-latinum) is located anteriorly within thepalatine at the level of the posterior root ofM1 (fig. 12) and is a single round opening oneach side (double bilaterally in CM 87973).Caudally, the pterygopalatine fissure is visi-ble on the lateral surface. The dorsal open-ings of the palatine foramina complex arevisible, corresponding to the fourth and fifthlateral palatine foramina described above,which are included in the sulcus that leads tothe caudal opening of the palatine canalrostrally. A sphenoidal process (processussphenoidalis) projects caudoventrally from

the external surface of the perpendicularpalatine lamina, contributing to the rostralportion of the tripartite ectopterygoid pro-cess (the pterygoid and the alisphenoidcontribute correspondent parts). The shapeof the internal surface of the perpendicularlamina is given by the roughly ellipticalperimeter of the choanae in the basiphar-yngeal canal. This shape is distorted by thenasal crest of the palatine ventrally and bythe sphenoid crest dorsally, which togethersplit the nasopharyngeal meatus into pairedopenings rostrally. The two perpendicularlaminae approach the presphenoid dorsallybut contact it only rostrally, leaving anoblique cleft that is continuous with thepterygopalatine fissure between the caudome-dial end of the palatine and the pterygoid.Another small vacuity is present in thetripartite space between the palatine, therostral end of the presphenoid, and the caudaledge of the wing of the vomer. The vomerinewing is overlapped slightly by the palatine,but this suture is barely visible externally.

LACRIMAL

The lacrimal (os lacrimale) is a paired,roughly pyramidal bone with an externaltriangular outline, located in the rostralmargin of the orbit (figs. 2, 12). The lacrimalhas two surfaces, orbital (facies orbitalis) andfacial (facies facialis), separated by the orbitalcrest (crista orbitalis). The lacrimal contactsthe palatine caudally, the maxilla rostrallyand ventrally (sutures described above), andthe frontal dorsally and caudally, formingthe frontolacrimal suture (sutura frontolacri-malis). The last one is squamous, roughlystraight on the rostral exposure, and crescen-tic (concave) and somewhat irregular in theorbit. The orbital rim crosses through thelacrimal, forming the orbital crest, a conse-quence of the two surfaces, facial and orbital,meeting at different inclinations. The facialsurface is level with the surface of therostrum, and the orbital surface lies insidethe orbit.

The major feature of the large facialexposure of the lacrimal is the lacrimalforamen (foramen lacrimale), the opening ofthe lacrimal canal (canalis lacrimalis) thatexpands in the fossa for the lacrimal sac


(fossa sacci lacrimalis). It is located anteriorto the orbital rim, immediately dorsal to thesuture with the maxilla, which participates inthe ventral margin of the foramen (fig. 12)but does not contribute to the lacrimal canal,which lies entirely within the lacrimal. Thedorsal margin of the lacrimal foramen ispoorly defined. Inside the orbit, there isa small, unnamed foramen that is connectedwith the major lacrimal foramen via anoblique, anterodorsally directed canal(fig. 12). On the basis of its content (seeForamina Contents and Homology), we termit here the vascular foramen of the lacrimal.The ventral margin of this foramen iscontributed by the maxilla on the left side.The orbital surface of the lacrimal is porous,with several minute foramina of irregulardistribution, whereas the facial surface issmooth. In CM 87973, there is a small, ovalopening in the suture between the rightorbital processes of the lacrimal and frontal,slightly below the level of the lacrimalforamen. Most specimens exhibit similaropenings, but a shallow pit (with no patentforamina) is present in this position on theleft side in CM 87973 and on both sides inCM 87972. Based on the study of thePteropus fetus, this opening transmits the m.obliquus ventralis and, therefore, is a lacrimalfenestra (Fig. 12; Wible and Gaudin, 2004).

JUGAL

The jugal bone (os zygomaticum) isa paired, small, laterally compressed elementlocated at the center of the zygomatic archbetween the anterior root of the arch(contributed entirely by the zygomatic pro-cess of the maxilla) and the posterior root(contributed entirely by the zygomatic pro-cess of the squamosal; figs. 2, 11). The jugalhas two surfaces, lateral (facies lateralis) andorbital (facies orbitalis), and two margins, thedorsal infraorbital margin (margo infraorbi-talis) and the ventral masseteric margin(margo massetericus). The zygomaticomaxil-lary suture is described above. The jugal hasa long, posteriorly directed process (processustemporalis) that articulates with the squamo-sal via the foliate temporozygomatic suture(sutura temporozygomatica). The lateral su-ture with the squamosal starts dorsally at

approximately one-third the length of thejugal, continuing diagonally down until theend of the jugal ventrally (at about themidpoint of the zygomatic process of thesquamosal). Medially, the jugal contributesa larger portion to the middle arch, but theshape of the suture with the squamosal is stillsimilar to the suture on the lateral surface,only slightly bowed dorsally. The dorsal freemargin of the jugal is short and extremelyirregular. Immediately dorsal to the masse-teric margin on the lateral surface is a notice-able longitudinal striation that runs thelength of the jugal, accompanied by anothershorter striation that is dorsal and anterior tothe major striation. In that area, the boneshows short, irregular incisive marks andsmall nutrient foramina. Based on the fetus,the m. masseter, pars profunda arises from themedial side of the zygoma and the superficialmasseter from the masseteric margin (anda very small part of the ventrolateral surface).The bulk of the lateral surface of the zygomain the fetus is free of muscle (see fig. 32),suggesting that all muscle attachment prob-ably lies ventral to the longitudinal striationin the adult. On the right side of CM 87972,there is a single nutrient foramen near thedorsal free edge of the jugal. The fetus alsohas one foramen that transmits a vein.

CRANIAL BONES (OSSA CRANII)

FRONTAL

The frontal bone (os frontale) is paired andforms the forehead of the skull (fig. 1) andthe bulk of the orbital wall (pars orbitalis ofthe frontal; fig. 2). In CM 87972, the frontalsare solidly fused with no trace of theinterfrontal suture (sutura interfrontalis, bywhich the left and right frontals articulatealong their midsagittal contact). The mostprominent feature of the frontal is the largepostorbital process (supraorbital or zygomat-ic process of the dog, processus zygomaticus).

In dorsal view (fig. 1), the frontal is a long,roughly rectangular plate (squama frontalis)with preorbital (pars nasalis), interorbital,and postorbital areas. Paired postorbitalprocesses project from the lateral border justcaudal to the midpoint of the dorsal length ofthe frontal. In the short preorbital area, the


frontal contacts the nasal, the maxilla, andthe lacrimal (sutures described above). Indorsal view, the interorbital area showsa slight but noticeable constriction. Thecircular orbital rim (margo orbitalis) con-tinues caudally in the caudoventrolaterallydirected postorbital process. The postorbitalprocess has a wide base that tapers caudallyto a blunt, squared-off tip (slightly bifid onthe right side). The free process overhangs theorbit by 2.3 mm in CM 87972, forminga small triangular roof over the posteriorhalf of the orbital concavity. The rostralmargin of the postorbital process is almoststraight in dorsal view, whereas the caudalmargin is deeply concave. In the rostralmargin on the left side is a minute, obliquenotch, accompanied by a sulcus, whichsuggests the passage of a nerve and/or vessel.Based on the Pteropus fetus, this notch andsulcus may accommodate the frontal nerveand vessels (see fig. 31).

Caudal to the postorbital process, thedorsolateral exposure of the frontal is broad-ly overlapped by a wedge-shaped rostralprocess of the parietal in the coronal suture(sutura coronalis, equivalent to the suturafrontoparietalis of the dog). This suture istherefore squamous. The suture lines fromeach side converge slightly until they abruptlyturn inward in a roughly right angle to meeteach other in the midsagittal line. This pointis located approximately midway between theroot of the postorbital process and theinterparietal.

The dorsal surface of the frontal showstwo prominent features: the postorbitalforamen and the frontal sinus. In the mid-point of the frontal length, on the rostral halfof the root of the postorbital process, thefrontal is pierced by the large postorbitalforamen. Each foramen is a slightly ovalopening that communicates the orbit with theskull roof. In close relationship with thepostorbital foramen, there are three (rightside of CM 87972) or four (left side) minuteforamina associated with the frontal diploicvein. The extra foramen on the left side openson the dorsal surface of the frontal, close tothe inner edge of the postorbital foramen.The frontal sinus (sinus frontalis) can bestudied because of the thinness of the frontalbone. Each of the paired sinuses is divided

into a medial and a lateral part. The latter isthe larger; it follows the orbital rim from thelacrimal to the postorbital foramen andshows a modestly swollen surface. As a con-sequence, the medial aspect of the interorbit-al surface is a slightly depressed passageconnecting the preorbital and postorbitalregions of the frontal. The medial part isnot swollen, but its extension can be seenbecause of the transparency of the bone; it isshort and placed medial to the anterior halfof the lateral part. Its anterior edge is definedby the sutures with the lacrimal, maxilla, andnasal; the posterior edge of each sideconverges in the midsagittal line. Posteriorto the postorbital processes, the surface of thefrontal is smooth and slightly domed.

The frontal occupies most of the orbitalwall, where it contacts the lacrimal rostrally,the palatine ventrally (sutures describedabove), and the orbitosphenoid caudally,forming the sphenofrontal suture (suturasphenofrontalis). The frontal also contactsthe parietal posterodorsally, continuing thefrontoparietal suture into the orbit (fig. 2).The sphenofrontal suture is squamous ven-trally, and it turns gradually plane dorsally.The shape of this suture resembles one side ofa lyre: it is convex caudoventrally, concavecaudodorsally, and gently rounded dorsallyas it curves posteroventrally to meet theparietal. The thinness of the bone in theorbital surface permits observation of struc-tures of the medial side of the orbital wall.There is a rostrally convex line running fromthe postorbital foramen to the point of triplearticulation between the frontal, the palatine,and the orbitosphenoid. This line marks theplacement of the cribriform plate of theethmoid (lamina cribrosa; see below). Fouroblique lines (the dorsalmost line is incom-plete) run between the line of the cribriformplate and the rostroventral limit of thefrontal. These are lines of internal attachmentof the ethmoturbinates (ethmoturbinalia),whose delicate laminae scroll inside the fiveinterlinear spaces. The surface between theline of the cribriform plate and the anteriororbital rim corresponds to a wide squamoussuture by which the frontal completely over-laps the ethmoid bone laterally, the fron-toethmoidal suture (sutura frontoethmoida-lis). The surface between the line of the


cribriform plate and the suture with theorbitosphenoid is smooth; its translucencereveals that it is devoid of bony structuresmedially. In the center of this area is thesmall, round, ventrally directed ethmoidalforamen (foramen ethmoidale). The ethmoi-dal foramen is very large in CM 87973 (largerthan the optic foramen; see Foramina) andopens between the frontal and orbitosphe-noid.

PARIETAL

The parietal bone (os parietale) is themajor element forming the skull roof (figs. 1,2). The braincase owes its bulbous shape(described above) chiefly to the curvature ofthe paired parietals. These protect the dor-solateral surface of the brain and providemost of the attachment area of the m.temporalis. In CM 87972, the surface ofthe bone is entirely smooth, so the limitsof the temporal fossa are not evident. Inadult Pteropus lylei (e.g., AMNH 237593)and most Pteropus species, however, thetemporal fossa is delimited by the sagittalcrest on the parietal (plus the infratemporalcrest of the alisphenoid and the nuchalcrest of the supraoccipital; see also Develop-ment).

The parietal has four borders: rostral orfrontal (margo frontalis), dorsal or sagittal(margo sagittalis), ventral or squamous(margo squamosus), and caudal or occipital(margo occipitalis). The parietals contact eachother in the corresponding sagittal borderthrough the sagittal suture (sutura sagittalis),and in turn each parietal contacts the frontalrostrodorsally (suture described above), theorbitosphenoid rostrolaterally, forming thesphenoparietal suture (sutura sphenoparieta-lis), the alisphenoid anteroventrally (thecontinuation of the sutura sphenoparietalis),the squamosal ventrally, forming the suturasquamosa, the interparietal mediocaudally(sutura parietointerparietalis), and the su-praoccipital laterocaudally, forming the occi-pitoparietal suture (sutura occipitoparietalisin Evans, 1993; part of lambdoid suture,sutura lambdoidea in the NAV). There is alsoa short contact with the mastoid exposure ofthe petrosal.

The sagittal suture is plane, slightly irreg-ular, and follows the midsagittal line withlittle deviation. The frontoparietal suture isdescribed above. The rostral border is anoblique suture directed caudoventrally; thesuture is squamous, with the parietal slightlyoverlapping the frontal and the orbitosphe-noid. The suture turns rostrally in its ventralquarter to meet the tripartite articulation ofthe orbitosphenoid, alisphenoid, and parietal.There the ventral border of the parietalbegins, as a sinusoidally shaped squamoussuture with the alisphenoid. The parietal isoverlapped by a rounded, dorsal process ofthe alisphenoid. The chief suture of theventral border is with the squamosal, whosedorsal lamina widely overlaps the parietal.The sutura squamosa is broadly wedge-shaped, with a straight anterior borderdirected dorsocaudally and a subtly convexposterior border directed ventrocaudally.Near the dorsal vertex of this triangle-shapedsuture lies the foramen for ramus temporalis,which is dorsally directed with two smallopenings in the left side and a single, largeropening in the right side. The foramina arebetween the squamosal and the parietal, witha short sulcus present in the parietal surfaceleading from the foramen. The suture withthe petrosal is , 2 mm in length. Next is thedorsomedially directed occipitoparietal su-ture. This is a squamous suture (with serratedborder) where the supraoccipital is slightlyoverlapped by the parietal. The parietointer-parietal suture shows the same structure; itscaudalmost extreme is at the tripartitearticulation of the parietal, supraoccipital,and interparietal. From this point, the sutureruns rostrodorsally, converging with its bi-lateral counterpart in the midsagittal line.The curvature of the suture, which describesan arch when both sides are taken together, issomewhat interrupted by a small ingressionof the parietal into the interparietal surfacenear the midsagittal line. This shows asa notch in the interparietal. In this smallregion are the first signs of fusion betweenthe interparietal and parietal on the left side.

Our study of the Pteropus fetus revealedanother part of the parietal that was notreadily apparent to us in our study of theintact adult skull (but see Internal Surfaces ofthe Skull). In the fetus, the parietal con-


tributes an epitympanic wing (sensu Mac-Phee, 1981): an exposure in the tympanicroof interposed between the sphenoid anteri-orly (the basisphenoid and alisphenoids arerepresented by a single ossification), thesquamosal laterally, and the tegmen tympaniof the petrosal posteriorly (see figs. 34, 35).This parietal epitympanic wing has a foramenand a sulcus associated with the ramussuperior of the stapedial artery (fig. 34).After this discovery, we subsequently identi-fied the parietal epitympanic wing on the leftside of CM 87973. It is a small, lobster claw–shaped exposure in the tympanic roof, withthe open end of the claw directed anterome-dially, positioned lateral to the posterolateralmargin of the piriform fenestra. It contactsthe alisphenoid anteriorly and medially, thepetrosal posteriorly, and is underlain laterallyby the squamosal. In the gap between theparietal epitympanic wing and the squamosalis the opening into a small vascular canaldirected posterodorsolaterally.

INTERPARIETAL

The interparietal (os interparietale) is anunpaired bone that forms the mediocaudalportion of the skull roof between the parietalsand the supraoccipital (fig. 1). The parietoin-terparietal suture is described above. Thesuture with the supraoccipital (unnamed inthe dog, because the interparietal is fusedwith the supraoccipital prenatally; Evans,1993) is termed here the occipitointerparietalsuture (sutura occipitointerparietalis), part ofthe lambdoid suture (sutura lambdoidea) inthe NAV, which has three sections: twobilateral portions that run from the tripartitepoint of articulation of the parietal, inter-parietal, and supraoccipital on each side,converging medially and slightly posteriorlyto meet a central portion that is essentiallyperpendicular to the sagittal axis and slightlyconcave. This suture is minutely serrated, andthere is no significant overlap between thetwo contacting bones. The surface of theinterparietal is smooth and somewhat domedover the central portion of the occipitointer-parietal suture, a feature accentuated in theadjacent area of the supraoccipital (seebelow). No foramina are found in theinterparietal.

PTERYGOID

The pterygoid bone (os pterygoideum) isa small, paired element located caudal to thepalatine in the basipharyngeal canal, ventralto the sphenoidal complex (figs. 3, 5, 10). Thepterygoid contacts the perpendicular processof the palatine rostrolaterally (suture de-scribed above), the presphenoid rostrome-dially, and the basi-alisphenoid complexdorsocaudally, forming the pterygosphenoidsuture (sutura pterygosphenoidalis). The pter-ygoid has two surfaces: a nasopharyngealsurface (facies nasopharyngea, medial andfacing the nasopharyngeal meatus) anda pterygopalatine surface (facies pterygopa-latina, lateral and facing the pterygopalatinefossa). It has a caudoventral angle orhamulus (hamulus pterygoideus; fig. 11), andthree processes seen in ventral view (fig. 10):rostromedial, lateral (ectopterygoid), andcaudal (all unnamed in the NAV).

The pterygopalatine surface of the ptery-goid is concave. Its rostral end projectslaterally and joins the respective processesof the palatine and alisphenoid that togetherform the ectopterygoid process. Caudal tothe ectopterygoid process, the lateral marginof the pterygoid runs beneath the sphenoidand describes a crescentic (concave) line thatends at the level of the caudal margin of theforamen ovale (see Alisphenoid and Foram-ina below). The pterygopalatine surface hasa small, round foramen in its center on theleft side and two smaller foramina in thesame place on the right side in CM 87972;based on the sectioned fetus, these foraminatransmit veins.

The medial surface of the pterygoid hasa rectangular rostromedial projection thatcontacts the presphenoid and the basisphe-noid. The medial surface is separated fromthe palatine rostrally by the pterygopalatinefissure. On both sides, there is a posteriorlydirected aperture in the midlateral part of thesuture with the basisphenoid. Extendinganteriorly from this aperture is a faint sulcuson the dorsal surface of the pterygoid openwithin the cranial cavity. The faint impres-sion of this sulcus is visible ventrally. Thisaperture represents the pterygoid canal (ca-nalis pterygoideus), which connects the basi-pharyngeal canal to the cavum epiptericum


(sensu Gaupp, 1902, 1905), the extraduralspace within the cranial cavity housing thetrigeminal ganglion. The rostromedial processhas a small foramen of uncertain function onits surface near the contact with the presphe-noid, almost obliterated on the left side.

The hamulus of the pterygoid is a low androunded process, laterally concave and slight-ly divergent caudally, that reaches its maxi-mum depth at its longitudinal midpoint andascends gently to the level of the basi-sphenoid as it continues posteriorly (figs. 10,11). The ventral margin is slightly thickened,forming an inconspicuous lip.

VOMER

The vomer is an unpaired bone of the nasalcavity. It consists of a sagittal part anda horizontal part (Evans, 1993). The formeris formed by two low, parallel laminae(laminae lateralis) that rest over the inter-maxillary suture, with deeply forked rostraland caudal ends, the incisive and sphenoidalincisures (incisura incisiva et sphenoidalis,respectively), and a ventral crest (cristavomeris). The dorsally opened structureformed by the laminae, the sulcus septi nasiof the dog or sulcus vomeris (septalis) of theNAV, receives the septal cartilage (septumnasi, its cartilaginous rostral part removed inCM 87972), which can be fully ossified in oldadults (e.g., AMNH 217045). The horizontalpart is formed by bilateral wings (alaevomeris). Only the rostral and caudal endsare accessible for examination through theexternal nasal aperture (fig. 4) and thechoanae, respectively. The incisive incisureis also visible through the incisive fenestra inventral view (figs. 3, 9). The ventral surfacewas examined in a disarticulated skull ofPteropus livingstonii (see fig. 24 and InternalSurfaces of the Skull).

Posteriorly, the caudal part of the vomer-ine wings has a dorsal point contact with thepresphenoid (sutura vomerosphenoidalis) onlyon the right side. The contact of the caudaledge of the vomerine wings with the faciesnasopharyngea of the perpendicular processof the palatine (sutura vomeropalatina dorsa-lis) is barely visible inside the nasopharyngealmeatus. No foramina are present in thevomer.

SPHENOID COMPLEX

The sphenoid complex comprises the un-paired presphenoid (os presphenoidale) andbasisphenoid (os basisphenoidale), and thepaired orbitosphenoids (ossa orbitosphenoi-dales) and alisphenoids (ossa alisphenoidales).Together, these bones constitute the rostraltwo-thirds of the basicranium. The presphe-noid is in the midline roof of the basiphar-yngeal canal (fig. 10); if fused to the orbito-sphenoids, as in CM 87972, it is called thecorpus of the os presphenoidale. The basi-sphenoid is in the midline of the basicraniumbetween the presphenoid and the basioccipi-tal; if fused to the alisphenoid, as in CM87972, it is called the corpus of the osbasisphenoidale. The orbitosphenoids arelocated dorsolateral to the presphenoid,projecting into the orbital wall; if fused tothe presphenoid, they are called the orbital(or lesser) wings of the (pre)sphenoid (alaeorbitales of the dog). The alisphenoids arelocated dorsolateral to the basisphenoid,forming the anteroventral side of the brain-case; if fused to the basisphenoid, they arecalled the temporal (or greater) wings of the(basi)sphenoid (alae temporales of the dog).The adjectives ‘‘lesser’’ and ‘‘greater’’ are oflittle value in megachiropterans because theorbitophenoids are unusually large bonesthat greatly exceed the alisphenoids in dorsalextension (figs. 2, 11). In CM 87972, con-spicuous sutures and gaps distinguish thepresphenoid + orbitosphenoid from the basi-sphenoid + alisphenoid, but there is noevidence of a division between the basi-sphenoid and alisphenoid, or between thepresphenoid and orbitosphenoid (nor aredivisions evident in the fetus examined; seefig. 32 and Skull Development). However,each of the four bones will be given a separatetreatment for descriptive purposes.

PRESPHENOID: The presphenoid is anelement whose nasopharyngeal exposure(the chief part visible externally) has a rhom-boidal shape with the rostral and caudal endstruncated (fig. 10). The presphenoid hasa point contact with the sphenoidal incisureof the vomer rostroventrally; it contacts thepalatine anterolaterally and the pterygoidposterolaterally (sutures described above).The rhomboidal shape of the ventral surface


of the presphenoid is due to the obliquecontacts of the palatines and pterygoids(fig. 10). The truncated anterior and posteriorsurfaces are perpendicular to the ventralsurface and are subcircular in shape. Thesesurfaces do not contact any bone rostrally orcaudally. The caudal surface matches a simi-larly truncated rostral end of the basisphe-noid, which reflects the loss of an interlock-ing cartilage in the macerated skull of CM87972 (the intersphenoidal synchondrosis).The ventral surface of the presphenoid isridged in the midsagittal line by the markedsphenoidal crest (crista sphenoidalis). Dorso-laterally, the presphenoid is fused to theorbitosphenoids, but the relationship of thesebones is best seen in orbital view (see below).No foramina are present in the presphenoid,although the optic canal lies between it andthe orbitosphenoid (see below).

ORBITOSPHENOID: The paired orbito-sphenoids form the caudal portion of theorbital wall, rising obliquely in the dorsolat-eral direction from their fused juncture withthe presphenoid to extend up to three-quarters of the orbital height (figs. 2, 11).The surface of the orbitosphenoid lies at anobtuse angle with the frontal in the orbitalwall. The orbitosphenoid contacts the frontalrostrally and dorsally, the parietal dorso-caudally (sutures described above), and thealisphenoid ventrocaudally, and it is fused tothe presphenoid ventrally. The orbitosphe-noid is overlapped by the parietal. The caudalmargin of the orbitosphenoid then contactsthe alisphenoid and is again fairly widelyoverlapped by this bone in a straight (rightside) or irregularly and slightly concave (leftside) suture. Ventrally, the orbitosphenoidfuses with the presphenoid rostral to the largesphenorbital fissure (see below).

The major feature of the orbitosphenoid isthe large, round optic canal (canalis opticus),which opens in the base of the bone. In thePteropus fetus, the presphenoid forms thefloor of the optic canal, the orbitosphenoidforms the roof; the anterior and posteriorwalls are cartilaginous. We are unsure exactlyhow this translates to the adult. In CM87972, there is a longitudinal ridge thatextends forward from the anteroventralmargin of the optic canal. In the fetus, thisridge, the cartilaginous ala hypochiasmatica,

provides attachment for extraocular muscles,and its base is formed by the presphenoid. Itseems likely that the presphenoid-orbito-sphenoid juncture in the adult is near thisridge. In CM 87972, the rostral edge of theoptic canal is deflected inward, and itsrostroventral edge becomes more prominentin lateral view. Caudal to the optic canal isthe rostral edge of the sphenorbital fissure,a large opening shared with the alisphenoidcaudally and floored by the rostromedialprocess of the pterygoid. The contour of therostral edge of the sphenorbital fissure ismore acutely concave in its dorsal portion. Inthe sphenorbital fissure coalesce the follow-ing foramina of the dog: the rostral alarforamen (foramen alare rostrale), the foramenrotundum, and the variably present foramenfor the zygomatic nerve.

BASISPHENOID: This bone forms thefloor of the braincase between the presphe-noid and the basioccipital, as well as the roofof the posterior part of the nasopharyngealmeatus (figs. 3, 10). The basisphenoid has anapproximately triangular shape defined bythe oblique suture with the rostromedialprocess of the pterygoid laterally (describedabove) and the perpendicular suture with thebasioccipital caudally. The bone is truncatedin its salient anterior end in the area wherea missing cartilage of the spheno-occipitaljoint (synchondrosis spheno-occipitalis) wasplaced (see Presphenoid). This truncation isdeeply concave in ventral view; it presentsa disklike surface in rostral view that matchesthe caudal end of the presphenoid. In thecaudal margin of the basisphenoid, thespheno-occipital synchondrosis is largelyplane, although the basisphenoid is slightlyoverlapped by the basioccipital on the lateralside of that perpendicular suture. This sutureis straight medially and is directed caudallytoward its lateral end, where it becomesinterdigitated. The ventral surface of thebasisphenoid is essentially flat medially;laterally, the basisphenoid is gently depressedalongside the oblique suture with the ptery-goid, and then it steadily descends behind theclosely adpressed pterygoid until reaching itsventralmost point at the level of the largeforamen ovale in the area of the alisphenoid.

Laterally, the basisphenoid is fused withthe alisphenoid; there is no trace of a suture


in the likely contact zone dorsal to thepterygoid and immediately caudal to itsposterior process. The rostral edge of thelarge piriform fenestra occurs in the posteriorportion of the basisphenoid-alisphenoid con-tact zone. The basisphenoid contacts theentotympanic (preserved only in the rightside in CM 87972) at the occipitosphenoidsuture (see Entotympanic). The only foramenpresent in the bony area attributed to thebasisphenoid is the carotid foramen (de-scribed with the Petrosal below).

ALISPHENOID: The alisphenoid is fusedseamlessly to the basisphenoid, and thereforemay be treated as a process of the basi-sphenoid (the above mentioned ala tempor-alis) for practical purposes. It contacts theorbitosphenoid rostrally, the parietal dorsal-ly, the pterygoid rostroventrally (all suturesdescribed above), and the squamosal caudo-ventrally, forming the sphenosquamosal su-ture (sutura sphenosquamosa), and it is fusedto the basisphenoid medially (fig. 10). Thebulk of the alisphenoid is in the infratem-poral fossa, whose limit with the temporalfossa above is obscurely marked by anincipient, roughly horizontal infratemporalcrest (crista infratemporalis) that divides thedorsal third from the ventral two-thirds ofthe alisphenoid (fig. 11). Except for this crest,the surface of the alisphenoid is entirelysmooth. As the alisphenoid extends rostro-dorsally, it bends following the curvature ofthe braincase; the infratemporal crest marksa sort of inflection point in the upwardcourse of the alisphenoid curvature. Thealisphenoid is widely overlapped by thesquamosal. The sphenosquamosal suture isroughly straight, caudoventrally directed,then horizontal from approximately the levelof the posterior edge of the foramen ovale(see below).

On the right side of CM 87972 andbilaterally in CM 87973, the alisphenoid hasa distinct process that partially divides thesphenorbital fissure into superior and inferiorhalves. This partial division reflects the situa-tion in the fetus, with its contents divided intodistinct superior and inferior bundles (seeForamina Contents and Homology).

The alisphenoid contributes to the rostralmargin of the piriform fenestra, which lies inthe juncture area of the basisphenoid and the

alisphenoid (figs. 3, 10). The posterior marginof the piriform fenestra is formed by thepetrosal. A shelf of bone from the ali-sphenoid is directed caudolaterally into thetympanic roof between the piriform fenestraand the ventral postglenoid area of thesquamosal. Based on CM 87973, this epi-tympanic wing of the alisphenoid has a pointcontact with the petrosal and a broadercontact with the epitympanic wing of theparietal.

Two salient features are present in thealisphenoid. First, there is a large, ellipticalopening, the foramen ovale (figs. 3, 5, 10, 11).This is a composite foramen, transmitting thecontents of the coalesced foramen ovale andalisphenoid canal (caudal alar foramen of thedog, foramen alare caudale; see ForaminaContents and Homology). Second, immedi-ately anterior to the rostral margin of theforamen, there is an anterolateroventrallydirected projection that contributes to thetripartite ectopterygoid process, formed bycontributions from the palatine, the ptery-goid, and the alisphenoid (figs. 3, 5, 10). Thealar canal of the dog runs right above thisprocess but outside the braincase, connectingthe foramen ovale with the sphenorbitalfissure (fissura orbitalis).

SQUAMOSAL

The squamosal (os temporale, pars squa-mosa) is a paired bone located laterally in thebraincase—the flattened squama—bearinga prominent process that arches rostrolater-ally, forming the posterior half of thezygoma—the zygomatic process (processuszygomaticus of the squamosal; figs. 2, 5, 11).Ventral to the root of the zygomatic processis the glenoid fossa (figs. 3, 5). The squamosalalso contacts the ectotympanic (annulustympanicus) in the opening of the externalacoustic meatus.

The squama is a lamina that widelyoverlaps the parietal dorsally, the alisphenoidrostroventrally (sutures described above),and the pars canalicularis of the petrosallaterally and caudally, forming the squamo-somastoid suture (sutura squamosomastoi-dea). The shape of the squama is triangularin its dorsal portion, with a vertex pointingdirectly dorsally at or near the foramen for


ramus temporalis in the sutura squamosa (seeabove). Caudally, the squama almost reachesthe incipient nuchal crest, overlapping thepars canalicularis and thus concealing thelateral exposure of the petrosal.

Projecting laterally from the squama is thezygomatic process. The process has a wide,roughly triangular root placed horizontallyjust rostral to the external acoustic meatus.The dorsal surface of the root is a depressionthat provides attachment for the m. tempor-alis. A small, rostrally directed foramen ispresent on both sides at the posteromedialbase of the zygomatic root (only on the rightside in CM 87973), and it communicates withthe postglenoid foramen (foramen retroarti-culare; see below). The sectioned fetus doesnot have a comparable foramen. In theventral surface of the zygomatic root is theglenoid fossa, formed entirely within thesquamosal; it is elliptical in shape, wider thanlong, and is limited anteriorly by the concaverostral margin of the zygomatic root, andposteriorly by the gradually sloping, bluntpostglenoid process (processus retroarticu-laris; see fig. 43). Immediately posterior tothe postglenoid process is the postglenoidforamen, a large, round, ventrally directedopening (figs. 3, 5, 10). Medial to the glenoidfossa, the squama shows a triangular laminathat overlaps the alisphenoid (suture de-scribed above). From the root, the zygomaticprocess arises as a thin bar of bone directedfirst laterally, then rostrodorsally. The pro-cess describes a low arch as it reaches theorbit, where it contacts the jugal. The jugalunderlies the anterior half of the zygomaticprocess (suture described above). As is thecase with the rest of the arch, the zygomaticprocess of the squamosal is laterally com-pressed and shows two surfaces: medial(facies medialis) and lateral (facies lateralis).Both surfaces are smooth. The dorsal marginof the process is thin, whereas the ventralmargin has a longitudinal concavity for theattachment of the m. massetericus.

The squamosal contributes the archeddorsal margin of the external acoustic mea-tus. The meatus begins rostrally immediatelyventral to the postglenoid foramen, where theanterior leg or crus of the ectoympanicattaches through ligaments (see below). Itends in the blunt posttympanic process

(processus retrotympanicus), located belowthe level of the opening of the postglenoidforamen, receiving ventrally the posterior legof the ectotympanic. The posttympanic pro-cess is buttressed medially by the posteriorcontinuation of the crista parotica of thepetrosal.

PETROSAL

The petrosal (os temporale, pars petrosa) isthe paired bone in the cranial base thathouses the organs of hearing and equilibra-tion. Two divisions of the petrosal aregenerally recognized: the more anteroventro-medial pars cochlearis, enclosing the cochlearduct and the saccule of the inner ear, and themore posterodorsolateral pars canalicularis,enclosing the utricle and the semicircularcanals.

In CM 87972, the petrosal has threesurfaces largely uncovered by other bones:the tympanic surface within the middle ear(facies tympanica of the dog), the cerebraland cerebellar surface within the cranialcavity (facies encephalica of the dog), andthe mastoid exposure on the occiput (proces-sus mastoideus of the dog). The pars co-chlearis has about a 2-mm-long, planecontact with the basioccipital medially, pointcontacts with the basisphenoid anterome-dially on either side of the carotid foramen,and a point contact with the alisphenoidanterolaterally at the posterolateral corner ofthe piriform fenestra. The pars canalicularis(via its concave, triangular facies occipitalis)contacts the exoccipital and supraoccipitalposteromedially, forming the occipitomas-toid suture (sutura occipitomastoidea), a foli-ate suture. Most of the lateral surface of thepars canalicularis, roughly trapezoidal inshape, is overlaid by the squamosal, formingthe squamosomastoid suture, a squamoussuture, at the junction of the occiput and thesidewall of the braincase, where the lateralaspect of the mastoid exposure abuts theposterior aspect of the squamosal. Betweenits contacts with the squamosal and thesupraoccipital, the pars canalicularis hasa short plane suture with the parietal. It alsohas about a 1-mm plane contact with theepitympanic wing of the parietal anterolat-erally. Finally, the petrosal has contacts with


the entotympanic, ectotympanic, incus, andstapes (see below). In CM 87972, fourapertures are found in the anterior andlateral borders of the petrosal. From ante-rolateral to posteromedial, these are thepiriform fenestra between the petrosal, basi-sphenoid, and alisphenoid; the carotid fora-men (foramen caroticum internum of the dog)between the petrosal, basisphenoid, andentotympanic; the basicochlear fissure (fis-sura petrooccipitalis) between the petrosaland basioccipital; and the jugular foramen(foramen jugulare) between the petrosal,exoccipital, and basioccipital (right sideonly).

Because much of the petrosal in the intactskull is not readily accessible for study, weuse as the centerpiece of our descriptionsisolated petrosals of Pteropus livingstoniiAMNH 274477, with differences from theCM P. lylei noted (figs. 13–15). The therianpetrosal is roughly the shape of a tetrahedronwith the following four surfaces: tympanic orventral, encephalic or dorsal, squamosal orlateral, and mastoid or lambdoid (MacIntyre,1972; Wible, 1990). We treat each of thesefour sides of AMNH 274477 separatelybelow.

In tympanic view, the most prominentfeature is the dome-shaped promontorium, themain part of the pars cochlearis (fig. 13). Thepromontorium is not a symmetrical dome; itslateral aspect is flatter than its medial, and itis longer than wide. The shape of thepromontorium is reflective of the enclosedcochlear duct, which Gray (1907) reported tobe two coils in Pteropus medius (5 P.giganteus), although he did not specify howthe measurements were made. Two aperturesare found in the posterior and posterolateralaspects of the promontorium: the roundwindow (fenestra cochleae) and oval window(fenestra vestibuli), respectively. The fenestracochleae is oval, wider than high, anddirected posteriorly and slightly ventrally. Itis closed in life by the secondary tympanicmembrane (membrana tympani secundaria).The dorsal margin of the fenestra cochleae isrecessed within a shallow cochlear fossula(sensu MacPhee, 1981), the posteroventralmargin of which is formed by the medialsection of the caudal tympanic process (seebelow). The cochlear fossula is broader in the

CM Pteropus lylei than in AMNH 274477.The fenestra vestibuli, which accommodatesthe footplate of the stapes, is also oval, witha stapedial ratio of 1.81 (length/width,according to Segall, 1970). The fenestravestibuli is directed laterally and slightlyventrally and sits within a shallow vestibularfossula (sensu MacPhee, 1981). The rim ofthe vestibular fossula has the same shape asthe oval window except for its ventralmargin, which is convex rather than concave.As a consequence of its position and orien-tation, the oval window is largely hidden indirect ventral view. At the anteromedialcorner of the promontorium is a small,triangular process that is directed anteroven-trally (apex parties petrosa). Based on CM87973, this process is underlain by the basi-sphenoid, and together these form the lateralmargin of the carotid foramen. The ante-rolateral surface of the promontorium hasa very shallow depression; based on thePteropus fetus (fig. 34), this is the fossa forthe m. tensor tympani (fossa m. tensor tympaniof the dog).

The ventral surface of the pars cochlearisin CM 87972 has an additional processwholly lacking from AMNH 274477. Thisprocess is a narrow, rounded shelf that isdirected ventromedially from the medialaspect of the promontorium. The anteriorend of this shelf is underlain by the en-totympanic. There is a shallow, longitudinalconcavity where this shelf meets the ante-romedial promontorial surface that is di-rected at the carotid foramen and representsa carotid sulcus. In CM 87973, this shelf ishypertrophied, being both wider and longer,and contacts the basisphenoid to contributeto the medial margin of the carotid foramen.

The bulk of the pars canalicularis intympanic view is represented by a broad shelflateral to the promontorium. Near the lateralmargin of this shelf is a sinuous ridge ofvarying height that extends the length of theshelf. The most prominent point on this ridgeis posteriorly, where there is a short processthat is directed toward, but falls short of, theback of the promontorium. This process isthe tympanohyoid or tympanohyal (tympa-nohyoideum), the ossified proximal segmentof Reichert’s (hyoid) cartilage; the ridge towhich the tympanohyoid is fused is the crista


parotica. The segment of the tympanohyoidproximal to the crista parotica is rod-shapedposteriorly, with a narrow anterior shelf.Distally, the rod-shaped part bifurcates intoa short anterior leg forming the medial edgeof the anterior shelf and a longer posteriorleg that tapers to a point. Based on CM87972, the posterior crus of the ectotympanicabuts the ventral surface of the proximaltympanohyoid. The crista parotica extendsboth anteriorly and posteriorly from thetympanohyoid. The sharp posterior continu-ation curves dorsally onto the mastoidexposure and is covered anterolaterally bythe posttympanic process of the squamosal.At the junction of the tympanohyoid and theposterior continuation of the crista paroticais the exit of the facial nerve from the middleear, the stylomastoid notch (foramen stylo-mastoideum in the dog). The more roundedanterior continuation of the crista paroticadecreases in height anteriorly and, oppositethe oval window, leads to a crescentic de-pression: the fossa incudis for the crus breveof the incus. The fossa incudis is not flat, butis angled such that its lateral aspect is dorsalto its medial aspect. Based on CM 87972, thesquamosal forms the stout lateral wall of thefossa incudis. The lower medial wall of thefossa incudis is formed by a sharp ridge thatis continuous with the crista parotica. Thisridge increases in height anteriorly, levels offto a flat area, and then decreases in height tothe anterolateral margin of the petrosal. Thisridge is the ventral edge of the tegmentympani, which is unusual in bats in that ithas a near vertical component rather thanmerely forming a horizontal roof over themiddle ear (Wible and Novacek, 1988; Wible,1992; Wible and Martin, 1993). As noted inother bats previously (Wible and Novacek,1988), in the Pteropus fetus, the tendon of them. tensor tympani wraps around the back ofthe ventral edge of the tegmen tympani(fig. 35), an arrangement that likely influ-ences the direction of muscle action.

Medial to the crista parotica and theventral edge of the tegmen tympani is a broadtrough that curves around the lateral marginof the promontorium (fig. 13). This troughextends nearly the length of the pars canali-cularis, but falls short of the anterolateralborder. Just behind that border, this trough

begins at a round, posteriorly directedforamen. This is the secondary facial fora-men, by which the facial nerve enters themiddle ear from the cavum supracochleare(Voit, 1909; geniculum canalis facialis). Form-ing the floor of the secondary facial foramenis a horizontal part of the tegmen tympanithat connects to the promontorium. Thetrough from the secondary facial foramento the stylomastoid notch is occupied by thefacial nerve and, therefore, is the facialsulcus. However, in the narrow intervalbetween the stylomastoid notch and theposterolateral margin of the petrosal, thetrough is occupied by the m. stapedius and,so, is the fossa for the m. stapedius (fossa m.stapedius of the dog).

The pars canalicularis in tympanic view isalso represented by a narrow shelf of boneposterior to the promontorium. The ventralmargin of this shelf is the medial section ofthe caudal tympanic process of the petrosal,or CTPP (sensu MacPhee, 1981), whichcontributes to the dorsal margin of thecochlear fossula. The medial section of theCTPP is concave and, in direct posteriorview, nearly completely shields the roundwindow from view. The CM Pteropus lyleidiffer from AMNH 274477 in their inflationof this region. The medial section of theCTPP is more bulbous, extending the poste-rior margin of the petrosal, and moreprominent, fully shielding the round windowin direct posterior view. Whereas the CTPP isa simple, concave ridge in AMNH 274477, inthe CM P. lylei the central portion of thisconcave ridge is raised, delimited by sharpedges, and resembles an anvil.

The encephalic view (fig. 14) is dominatedby two large depressions, the smaller internalacoustic meatus (meatus acusticus internus)anteroventromedially and the larger subarc-uate fossa (fossa subarcuata) posterodorso-laterally. The former lies in the pars co-chlearis and the latter in the parscanalicularis. An oblong aperture (porusacusticus internus) leads into the internalacoustic meatus, which is divided intosuperior and inferior fossae by a low trans-verse crest (crista transversa). The smallersuperior fossa (foramen acusticum superius)includes the facial nerve area (area nervusfacialis) anterolaterally and the dorsal vestib-


ular area (area vestibularis superior) poster-omedially, for passage of the facial nerve andpart of the vestibular nerve, respectively. Theinferior fossa (foramen acusticum inferius)includes the large, kidney-shaped cochleararea (area cochleae) and the small, roundventral vestibular area (area vestibularis in-ferior), for the cochlear nerve and the re-mainder of the vestibular nerve, respectively.Within the cochlear area is the spiral tract ofminute foramina (tractus spiralis foramino-

sus) for the fascicles of the cochlear nerve.The subarcuate fossa, which houses theparaflocculus of the cerebellum, is a deep,wide depression that occupies a considerableportion of the pars canalicularis. Leadinginto the subarcuate fossa is a kidney-shapedaperture that is narrower than the subarcuatefossa proper. Because of the thinness of thebone, the posterior semicircular canal (canalissemicircularis posterior) and the crus com-mune (crus osseum commune), which lie in the

Fig. 13. Pteropus livingstonii AMNH 274477, left petrosal bone in oblique ventral view (tympanicsurface). Scale 5 1 mm. Abbreviations: app apex parties petrosa; cp crista parotica; ctpp caudal tympanicprocess of petrosal; fc fenestra cochleae; fi fossa incudis (medial wall); fs facial sulcus; fv fenestra vestibuli;ji jugular incisure; me mastoid exposure of petrosal; pp paroccipital process of petrosal; pr promontoriumof petrosal; sf stapedius fossa; sff secondary facial foramen; smn stylomastoid notch; th tympanohyoid; tttegmen tympani; ttf tensor tympani fossa.


rim of the subarcuate fossa, are visible. Alsovisible is the part of the anterior semicircularcanal (canalis semicircularis anterior) proxi-mal to the crus commune.

Three additional apertures are visible onthe encephalic surface (fig. 14). The largest ofthese is on a narrow shelf of bone ante-rolateral to (and sloping away from) the

Fig. 14. Pteropus livingstonii AMNH 274477, left petrosal bone in dorsal view (encephalic surface).Scale 5 1 mm. Abbreviations: app apex parties petrosa; asc anterior semicircular canal; av aqueductusvestibuli; cc cochlear canaliculus; crc crus commune; ct crista transversa of petrosal; fai foramen acusticuminferius; fas foramen acusticum superius; fcb fossa cerebellaris; hF hiatus Fallopii; iam internal acousticmeatus; ji jugular incisure; pfc prefacial commissure; psc posterior semicircular canal; saf subarcuate fossa;scev sulcus for capsuloparietal emissary vein; tt tegmen tympani.


foramen acusticum superius and is partiallyhidden in direct dorsal view by the bar ofbone (prefacial commissure) forming thelateral margin of the internal acoustic mea-tus. This anteriorly directed, oval aperture isthe hiatus Fallopii, the anterior opening ofthe cavum supracochleare. Based on CM87971, part of the shelf of bone posterolateralto the hiatus Fallopii is covered by theparietal (see below). The second aperture ison a narrow shelf of bone posteromedial tothe foramen acusticum inferius the jugularincisure (incisura jugularis). This foramen isalso partially hidden in direct dorsal view asit faces posteromedially into the jugularforamen. This is the opening by which theperilymphatic duct (ductus perilymphaticus)enters the petrosal, the cochlear canaliculus(apertura externa canaliculus cochleae). Thethird aperture is on a narrow shelf medial tothe subarcuate fossa. This shelf has a faintdepression, the fossa cerebellaris, and in theposterior part of this fossa is the oval,posteriorly directed opening by which theendolymphatic duct (ductus endolymphaticus)enters the petrosal, the vestibular aqueduct(apertura externa aqueductus vestibuli). Ashallow sulcus leads into the vestibularaqueduct from behind. Lastly, posterodorsalto the subarcuate fossa (and running parallelto it) is a short, very shallow sulcus for thecapsuloparietal emissary vein (sinus tempor-alis).

The most dominant feature in squamosalview (fig. 15) is the trapezoidal surfacecovered by the squamosal in the intact skull.The irregular ventral margin of this surface isformed by the crista parotica posteriorly andthe tegmen tympani anteriorly. The poster-oventral aspect of this surface has a noticeablebulge, which in the intact skull is covered bythe posttympanic process of the squamosal.This bulge corresponds in position to themastoid process (processus mastoideus inSchaller, 1992). As noted by MacPhee(1981), that term has been used for a varietyof probably non-homologous bumps on thepetrosal. Following Wible and Gaudin(2004), we prefer the term paroccipital pro-cess for this bulge. The anterodorsal aspect ofthe trapezoidal surface has a very shallowsulcus for the capsuloparietal emissary veinthat is continuous with the sulcus reported on

the encephalic surface. Anterior to thetrapezoidal squamosal surface is a roughlytriangular surface whose vertex is the ventraledge of the tegmen tympani. The ventral halfof this shelf is covered by the parietal, basedon CM 87971.

The mastoid exposure of the petrosal(figs. 5, 13, 15) is roughly rectangular, tallerthan wide. Dorsally, it contacts the parietallaterally and the supraoccipital medially. Thecontact with the parietal is shorter (ca. 2 mm)and straight; that with the supraoccipital (ca.3 mm) is sinuous, with a degree of interdig-itation. Medially, the mastoid exposure con-tacts the exoccipital at a slightly concavesuture; this joint shows some interdigitationin the dorsal part. Laterally, it contacts thesquamosal at a convex suture. The freeventral margin is concave, with a sharpprominence in the ventrolateral corner,the posterior continuation of the cristaparotica. In CM 87973, a distinct ridgecurves dorsomedially from the ventral endof the posterior continuation of the cristaparotica and continues onto the paracondy-lar process of the exoccipital; this ridge isvery faint in AMNH 274477. Based on thefetus, the m. sternomastoideus (Evans, 1993;musculus sternocephalicus, pars mastoidea inthe NAV) attaches to this ridge, the post-tympanic process of the squamosal, and theparacondylar process of the exoccipital. Atthe dorsomedial corner of the mastoidexposure in CM 87972 is a small mastoidforamen (foramen mastoideum), which is0.4 mm on the left and smaller on the right.The petrosal only contributes to the borderof the left mastoid foramen. Based onPteropus capistratus AMNH 194276, themastoid foramen is at the junction of theexoccipital and supraoccipital with the mas-toid exposure.

ENTOTYMPANIC

A rostral entotympanic (rostrales entotym-panicum of Klaauw, 1922) is present inPteropus, including the species describedhere. Novacek (1980, 1991) figured therostral entotympanic in P. poliocephalus. Thistiny, peglike element is located in thebasicranium ventral to the juncture of thebasisphenoid and basioccipital, at the basico-


chlear fissure (it is lost from the left side ofthe macerated skull of CM 87972). The bonepresents a roughly tetragonal shape (figs. 3,5, 10). The medial, roughly triangular surfacehas a concave caudal margin and a rostro-dorsal vertex. The base of the entotympanicunderlies the occipitosphenoid suture; thelateral and caudal sides are partially hidden.The shape is far more irregular in otherspecimens, and in AMNH 237596 the rightentotympanic is divided in two parts. In adultspecimens, when it is preserved, the entotym-panic may be caudally displaced, reaching thepetrosal and even fusing to it, while losingcontact with the basisphenoid and exoccipital(e.g., in AMNH 237593). In the Pteropusfetus, the cartilaginous rostral entotympanicis an irregular U-shaped structure that sitsbeneath the anterior pole of the promontor-ium (see reconstruction in Wible and Martin,

1993: fig. 6). The main body of the rostralentotympanic lies anteriorly (below the ca-rotid foramen in fig. 33) and has twoposteriorly directed curved arms, one ventro-medial and the other dorsolateral (theposterior end of which is seen in fig. 34).

In addition to a rostral entotympanic, thePteropus fetus has a flat cartilaginous caudalentotympanic (caudales entotympanicum ofKlaauw, 1922), longer than wide, whichabuts the medial aspect of the posterior crusof the ectotympanic and fills in the spacebetween that bone, the promontorium, andthe rostral entotympanic (figs. 33–35; seereconstruction in Wible and Martin, 1993:fig. 6). There is no trace of this element inthe osteological specimens, which suggeststhat, unlike the rostral entotympanic, thecaudal entotympanic does not ossify in theadult.

Fig. 15. Pteropus livingstonii AMNH 274477, left petrosal bone in lateral view (squamosal surface).Scale 5 1 mm. Abbreviations: app apex parties petrosa; cp crista parotica; fi fossa incudis; hF hiatusFallopii; me mastoid exposure of petrosal; pfc prefacial commissure; pp paroccipital process of petrosal; prpromontorium of petrosal; scev sulcus for capsuloparietal emissary vein; th tympanohyoid; tttegmen tympani.


ECTOTYMPANIC

The ectotympanic (annulus tympanicus) isa small, ring-shaped bone located ventral tothe concave margin of the squamosal be-tween the postglenoid and posttympanicprocesses, in the dorsal border of the externalacoustic meatus (joint unnamed in theNAV; figs. 2, 3, 5). The ectotympanic iselliptical in shape (fig. 16A, B) and conspic-uously inclined ventromedially (figs. 3, 16C,43). In ventral view, the annulus steadilyincreases in width rostrodorsally (fig. 3).Its irregular medial margin has a smalllamina flaring medially (fig. 3; the styliformprocess of Henson, 1970). The annulus ishorseshoe-shaped and has two archingbranches (crura), anterior and posterior,that are continuous ventromedially (fig. 16).The crus anterior abuts the medial marginof the squamosal and extends its contactfrom the level of the rostral edge of thepostglenoid foramen to beyond the midpointof the arch of the external acoustic meatus(fig. 2). The lateral margin of the anteriorcrus is thickened. The crus posterior isnoticeably thinner, and it has a restrictedarea of contact with the tympanohyoid (seePetrosal). The crura do not contact eachother dorsolaterally, being separated bya space of ca. 1 mm. The annulus has a deepmedial sulcus (sulcus tympanicus) that isroughly constant in width throughout(fig. 16C). The tympanic membrane (mem-brana tympani) attaches to the medial borderof the sulcus. The ectotympanic and tympan-ic membrane form the lateral limit of thetympanic (or middle ear) cavity (cavumtympani).

In CM 87972, both ectotympanics are inplace, precluding a full view of the medialaspect of the bones. Examination is possiblein Pteropus livingstonii AMNH 217044,whose ectotympanics are detached from theskull base. In this specimen, the ectotympanicshows a slightly expanded medial border withthe small flange described above projectingdirectly medially. Dorsally, the rostral pro-cess of the malleus (see below) overhangs theanterior crus. The rostral process is fusedventrally to the anterodorsal surface of theanterior crus medial to the raised lateralborder of the crus. Seams are clearly visible in

the contact of the rostral process and theanterior crus.

MIDDLE EAR OSSICLES

The three middle ear ossicles (ossiculaauditus)—the malleus, the incus and thestapes—lie in the tympanic or middle earcavity (cavum tympani in the auris media). Asin mammals in general, the malleus is formedembryologically by two components from thefetal lower jaw (Klaauw, 1922; Jurgens,1963). The malleus per se is derived fromthe articular. The second element is therostral or anterior process, which is contin-uous with the malleus (hence the term outerlamella of processus gracilis in Jurgens, 1963)and homologous to the gonial bone (5prearticular). The incus (derived from thequadrate) and the stapes successively trans-mit sound to the inner ear through thefenestra vestibuli of the petrosal. Doran(1878) gave a rather superficial descriptionof the malleus, incus, and stapes of Pteropus,based on P. hypomelanus and P. edulis (mostlikely a synonym of P. vampyrus), and Wassif(1948) provided a detailed description of theossicles in Rousettus aegyptiacus. A descrip-tion of the three bones, based on P. lylei andP. livingstonii, follows.

MALLEUS: The malleus (fig. 16A–C), thefirst bone in the ossicular chain, articulateswith the incus, forming the incudomalleolarjoint (articulatio incudomallearis), reported tobe a synovial joint in Pteropus giganteus(Hinchcliffe and Pye, 1969). The malleus hasa head (caput mallei) with a large articularfacet for the incus, an osseous lamina whosecaudal margin is the neck (collum mallei),a rostral or anterior process (processusrostralis), a manubrium (manubrium mallei),a lateral process (processus lateralis), and anorbicular apophysis.

The dorsalmost part of the malleus is thehead—a roughly conical process with theapex directed rostroventrally. The head ishollowed ventrally, resulting in a hoodlikeappearance, where the head receives thelateral ridge of the rostral process in itsventral cavity (see below). Caudal to the headis the concave facet for the incus, which hastwo surfaces—a wide, oblique caudodorsalsurface and a narrow caudoventral portion—


meeting at a roughly 90 degree angle. Ventralto the head is the osseous lamina of themalleus; it is a deep and thin plate of bonethat buttresses the rostral process rostroven-trally and joins the manubrium ventrally.Laterally, the osseous lamina is framed bytwo thick borders: one in the ventral marginof the lamina, and the other, deeply convexcaudally, in the caudal margin reaching thehead of the malleus (the neck). Medially, theosseous lamina shows a smooth and slightlyconvex surface. The m. tensor tympaniattaches in the caudal area of the medialsurface; there is only a faint scar thatindicates the site of attachment (i.e., a con-spicuous processus muscularis is absent). Atthe ventralmost point of the osseous lamina,three heterogeneous processes arise indifferent directions: laterally, the lateral pro-cess; caudally, the orbicular apophysis;and ventrocaudally, the manubrium. Thelateral process is a short, somewhat ellipticaleminence oriented dorsoventrally that iscontinuous with the lateral margin of themanubrium. The slightly larger orbicularapophysis also has an elliptical base, later-omedially oriented, whose domed top facescaudally. The orbicular apophysis shows anirregular depression in its caudal side. Inturn, the lateral process hides a deep fossain its medial contact with the osseouslamina. The long, swordlike manubrium isa rostrocaudally flat process with a smallspatulate end that attaches to the tympanicmembrane. In caudal view, the manubrium iswide at the level of the orbicular apophysis.The lateral margin of the manubrium isalmost straight, whereas the medial marginis dorsally convex and becomes almoststraight ventrally as it reaches the end ofthe process.

The rostral process of the malleus consistsof a horizontal inner lamella, correspondingto the rostral process of the malleus per se,and a partly vertical outer lamella, corre-sponding to the gonial (Jurgens, 1963). Thelimits of the two areas cannot be establishedprecisely in our specimens. The rostral pro-cess as a whole is a large, dorsally concavelamina with a curving lateral border thataccompanies the lateral border of the ecto-tympanic, and a low and wide medialportion. From the rostral end, the lateral

Fig. 16. Pteropus livingstonii AMNH 274466,medial (A), lateral (B), and oblique dorsal (C)views of the right (A and C) and left (B)ectotympanic and articulated malleus and incus(broken). Scale 5 1 mm. Abbreviations: alecanterior leg of ectotympanic; attm attachment oftensor tympani muscle; cty crista tympanica; fctnforamen for the chorda tympani nerve; hm head ofmalleus; in incus; lm lamina of malleus; lpm lateralprocess of malleus; mam manubrium of malleus;nm neck of malleus; oam orbicular apophysis ofmalleus; plec posterior leg of ectotympanic; rpmrostral process of malleus; st sulcus tympanicus.


border rises caudally as a roughly verticalridge that remains level throughout until it isslightly upturned immediately ventral to thehead of the malleus. The ridge is thin, with itsdorsal margin strengthened by a longitudinalthickening of the bone. Medially, the laminadescends into a shallow basin with its widestportion roughly at the caudal two-thirds ofits length. At this point, in the medial border,the lamina has a shallow depression anda small rounded prominence. From thatpoint caudally, the lamina conspicuouslydecreases in breadth to meet the outer lamellaventral to the head. Rostrally, the laminadevelops a shallow sulcus that ends at itsapex. Based on Rousettus (Jurgens, 1963:fig. 11), this sulcus held Meckel’s cartilage

in the fetus, and based on the Pteropusfetus it also held the chorda tympaninerve. The medial border of the lamina isconvex, growing thicker to form a torusmedially. The rostral process is pierced bythe foramen for the chorda tympani nerve,a small oval opening in the substance ofthe lamina (figs. 16C, 35). This opening isslightly rostrodorsally oriented. Ventrally,the rostral process is ankylosed to the dorsalsurface of the anterior crus of the ectotym-panic.

INCUS: The incus (fig. 17A–D), thesecond bone in the ossicular chain, articulateswith the stapes, forming the incudostapedialjoint (articulatio incudostapedia), reportednot to be a synovial joint in Pteropus

Fig. 17. Pteropus livingstonii AMNH 274466, diverse views (A to D) of the isolated left incus. Whenarticulated, the long crus (lcin) points medially and the short crus (scin) points dorsally. Scale 5 0.2 mm.Abbreviations: aplin attachment of posterior ligament of incus; ein unnamed round eminence of incus; famincudal facet for head of malleus; lcin long crus of incus; lp lenticular process of incus; scin short crusof incus.


giganteus (Hinchcliffe and Pye, 1969). Theincus of AMNH 240006 was examined insitu, whereas the incus of AMNH 237596 wasobserved isolated. The incus has two stoutlegs, short (crus breve) and long (cruslongum), connected by an incudal body(corpus incudis) that contains the facet forthe malleus. The two crura diverge from oneanother nearly at right angles. The short cruspoints dorsally and slightly caudally into thefossa incudis (described with the Petrosalabove) and has a simple, conical shape witha truncated apex. The strong posteriorligament (lig. incudis posterius), which fixesthe incus to the roof of the fossa incudis, iseasily seen in situ in AMNH 240006. Thelong crus points caudally and slightly ven-trally, and it is compressed and rotated as itbends medially to meet the stapes. The tip ofthe long crus is expanded in the rounded,medially flattened lenticular process (proces-sus lenticularis), which matches the head ofthe stapes. The incudal body has a large facetfor the malleus, with the ventral half concaveand the rostral half less so. The articularsurface is rugose; the ventral part has a tri-angular shape with the vertex directedcaudally, and the caudal part is semicircularwith the arch directed dorsally and a concaveventral margin. Ventrolaterally, the incudalbody presents a rounded eminence limitedventrally by the border of the facet for themalleus and dorsally by a shallow circularfossa. This fossa is less marked in otherspecimens examined (e.g., P. lylei AMNH237596).

STAPES: The stapes transmits vibrationsfrom the incus to the fenestra vestibuli of thepars cochlearis of the petrosal in the syndes-mosis tympanostapedia. The stapes was ex-amined in situ in AMNH 240006 and ex situin AMNH 274470 (fig. 18; a stapes is figuredfor Pteropus edulis by Doran, 1878: figs. 26,27). It consists of a base or footplate (basisstapedis), two crura or legs—anterior orrostral (crus rostrale) and posterior or caudal(crus caudale)—a stapedial or intracruralforamen between the legs and base, anda neck and head (caput stapedis; fig. 18). Thebase is elliptical in shape with the major axisrostrocaudally oriented, articulating with theedge of the fenestra vestibuli of the petrosal.The anterior leg is very thin and slightly

bowed rostrally, and it reaches the basewith little change in diameter. The posteriorleg is at least twice as thick as the anteriorleg, slightly wider medially, where it isalmost as wide as the base, and it is roughlystraight save for the rostral margin (facingthe stapedial foramen), which is noticeablyconcave. The two legs connect laterallyin a short neck, from which the smallmuscular process for the attachment ofthe m. stapedius projects caudally. Thismuscular process is roughly triangular inshape, and it has a caudal surface placedobliquely with respect to the plane of thehead. The head is a flat piece wider than theneck, of round shape in lateral view, thatarticulates with the lenticular process ofincus. The head exhibits a rugose dorsalsurface whose caudal margin gently turnsmedially, being virtually continuous with thecaudolateral surface of the muscular process(fig. 18).

Fig. 18. Pteropus livingstonii AMNH 274466,dorsal view of the left stapes. Scale 5 0.1 mm.Abbreviations: alst anterior leg of stapes; bst baseof stapes; hst head of stapes; icf intercruralforamen; mpst muscular process of stapes; nstneck of stapes; plst posterior leg of stapes.


OCCIPITAL COMPLEX

The occipital complex (os occipitale) isformed by the unpaired basioccipital (parsbasilaris) and supraoccipital (squama occipi-talis), and the paired exoccipitals (parslateralis; fig. 5). These four embryologicalunits, each ossified from separate centers,surround the foramen magnum, which con-nects the brain with the spinal cord andassociated structures (fig. 5). The bones arefused seamlessly in CM 87972 except fortraces of a suture between the basioccipitaland exoccipitals in the medial margin of thejugular foramen (see fig. 5 and below). Forthat reason, precise relationships amongthese bones will be discussed based onPteropus capistratus AMNH 194276, a youn-ger specimen in which all sutures are present,in the Skull Development section.

BASIOCCIPITAL: This bone has a roughlyrectangular form and contacts the basisphe-noid rostrally (suture described above), theexoccipital caudolaterally, forming the ven-tral intraoccipital synchondrosis (synchondro-sis intraoccipitalis basilateralis), and the parscochlearis of the petrosal, forming theposterior basicochlear commissure laterally(figs. 3, 5), the latter being the petro-occipitaljoint of the dog (Evans, 1993; synchondrosispetro-occipitalis). The lateral margin of thebasioccipital forms the medial margin of thebasicochlear fissure (the petro-occipital fis-sure of the dog) rostrally and the jugularforamen (foramen jugulare) caudally, withboth openings separated by the relativelynarrow posterior basicochlear commissure.The basicochlear fissure is coalesced with thepiriform fenestra and the carotid foramenlaterally, although the openings are incom-pletely delimited by processes of the rostro-lateral angle of the basisphenoid and thepetrosal (fig. 10). The medial margin of thebasicochlear fissure occupies roughly theanterior third of the lateral margin of thebasioccipital. The posterior basicochlearcommissure is a rather irregular bridge ofbone that loosely connects the basioccipitaland the pars cochlearis of the petrosal. Thebasioccipital component of the posteriorbasicochlear commissure is roughly straight,slightly divergent, and essentially featureless(cf. the dog, in which a muscular tubercle is

present in this area). The commissure isapproximately as long as the basicochlearfissure. Just past the posterior basicochlearcommissure caudally, the basioccipital pene-trates slightly into the opening of the jugularforamen on the right side, whereas it isexcluded from the foramen by the exoccipitalon the left side. In this area is the trace of theventral intraoccipital synchondrosis, , 1 mmin length and directed posteromedially, deep-ly incised only in the immediacy of thejugular foramen. The caudal margin of thebasioccipital participates in the ventral mar-gin of the foramen magnum at the concaveintercondyloid notch (incisura intercondyloi-dea). The surface of the basioccipital isventrally curved, with the curvature accentu-ated toward the caudolateral angle. Thesurface is marked medially by a low crestthat extends posterolaterally and that isequivalent to the pharyngeal tubercle of thedog (tuberculum pharyngeum). This ill-de-fined tubercle divides the basioccipital intotwo parts; rostrolateral to this crest are theshallow, faint marks of the paired, roundedbasioccipital pits, which are sites of attach-ment of the m. longus capitis and the m. rectuscapitis ventralis (figs. 34, 35).

EXOCCIPITAL: The paired exoccipitalsare located posterolateral to the basioccipitalon the ventral side of the cranium and lateralto the foramen magnum on the occipital sideof the cranium (fig. 5). The ventral portionhas a deeply concave lateral margin thatcorresponds to the medial margin of the largejugular foramen. Caudomedial to the jugularforamen is the round hypoglossal foramen(canalis nervus hypoglossum of the NAV andforamen hypoglossi of the dog). The hypo-glossal foramen opens ventrolaterally and,based on Pteropus capistratus AMNH194276, it lies entirely within the exoccipital.Caudal to the jugular foramen is the para-condylar process (processus paracondylaris),a ventral projection from which the m.digastricus originates. The process is broadat its base, tapering to a hooklike, rostrallydirected point. Lateral to the paracondylarprocess is the convex suture with the mastoidexposure of the petrosal, the occipitomastoidsuture. Medial to the paracondylar process isthe relatively deep ventral condyloid fossa(fossa condylaris ventralis).


Lateral to the foramen magnum andmedial to the condyloid fossa are theprominent occipital condyles (condyli occipi-tales), the cranial components of the atlanto-occipital joints (articulatio atlanto-occipita-lis). The condyles are elliptical, taller thanwide, and obliquely placed such that theirdorsal ends are widely divergent and welloutside the dorsolateral margin of the fora-men magnum. By contrast, the ventral endsare placed on the arch of the margin of theforamen magnum. The epiphyseal cartilage(cartilago epiphysealis) is present as a whitishcap covering most of the surface of thecondyle. The outline of the foramen magnumdorsal to the condyles is somewhat triangularwith the dorsal vertex rounded; based onPteropus capistratus AMNH 194276, only thedorsolateral portion of this outline lies withinthe exoccipital, the dorsalmost portion beingwithin the supraoccipital (fig. 43A, but seeSkull Development). Two minute nutrientforamina are located symmetrically on eachside of each condyle. A third one is ventral tothe lateral nutrient foramen of the left side.Laterally, in the tripartite joint between thepetrosal, exoccipital, and supraoccipital, isthe small, receding mastoid foramen, whichopens caudomediodorsally. On the right side,the petrosal is excluded from the opening.The exoccipital is fused without a trace withthe supraoccipital in CM 87972; based on P.capistratus AMNH 194276, the dorsal in-traoccipital synchondrosis (synchondrosis in-traoccipitalis squamolateralis) is a relativelyacute arch that rises between the mastoidforamen and a point in the dorsal two-thirdsof the supracondylar outline of the foramenmagnum (see fig. 43A). This area corre-sponds to the dorsal condyloid fossa of thedog (fossa condylaris dorsalis), but in CM87972 it is only minimally depressed.

SUPRAOCCIPITAL: This bone occupiesthe dorsal part of the occiput, participatingin the dorsal margin of the foramen magnum,and bears the incipient lamboid or nuchalcrest (crista nuchae). The supraoccipital con-tacts the exoccipitals ventromedially, themastoid exposure of the petrosal ventrolat-erally, the parietal dorsolaterally, and theinterparietal dorsomedially (all sutures de-scribed above; fig. 5). The nuchal crest ismodestly marked as two low arches that meet

at the midsagittal line. The crest as a wholedivides the supraoccipital into roughly equaldorsal and ventral parts. The dorsal surface isengraved with short incisions that may havebeen numerous nutrient foramina and theirshort accompanying sulci. On each side, thenuchal crest is continued laterally into themastoid exposure of the petrosal. The su-praoccipital is domed along the midsagittalline. The round and low external occipitalprotuberance (protuberantia occipitalis ex-terna) is located between the occipitointer-parietal suture and the nuchal crest. It iscontinued ventrally by a narrower, shallowcrest, the external occipital crest (cristaoccipitalis externa), a smooth median ridgethat inconspicuously reaches the foramenmagnum.

MANDIBLE

The mandible (mandibula) or dentary boneis paired, bears the lower dentition, andforms a lever that allows for mechanicalprocessing of food in the mouth. Eachmandible is formed by a horizontal, tooth-bearing body (corpus mandibulae) and a cau-dal ramus (ramus mandibulae; figs. 6, 7). Theleft and right mandibles diverge caudally atca. 30 degrees, forming between them theintermandibular space (spatium mandibulae,regio intermandibularis) where the tongue lies.The mandibles are fused anteriorly withouta trace of a suture at the mandibularsymphysis (symphysis mandibulae).

The body of the mandible (fig. 6) isa relatively thick, bony bar that presents analveolar surface dorsally (margo alveolaris),two vertical surfaces—lingual (facies lin-gualis) and buccal (facies buccalis)—a mentalsurface (facies labialis), and a ventral border(margo ventralis). The alveolar surface con-tains the alveoli for two incisors (i1, i2),a canine (c), three premolars (p1, p3, p4), andthree molars (m1–3). There are two smalldiastemata, one between the left i1 and theright i1, and the other between p1 and p3.There are no other marked interdentalspaces, but there is a narrow retromolarspace between m3 and the ramus. In lateralview, the alveolar line shows a deep emargi-nation that houses the large lower canine.The alveolar line is flat (straight) from the


canine to the level of p1, after which it takesthe shape of a progressively attenuatedsinusoid whose peaks occur between theroots of the cheek teeth and whose valleyscorrespond to the interdental spaces (septainteralveolaria). The oscillation of the alveo-lar line is flattened behind m1, from which itcontinues smoothly into the dorsal border ofthe ramus, outlining an uninterrupted as-cending profile. The buccal surface of the

body is formed by semitranslucent bonethrough which the roots of p3 and p4 areclearly visible, but the surface itself is smooth(no juga are present). The most noteworthyfeature of the buccal surface is the posteriormental foramen (foramen mentale, the homo-logue of the middle mental foramen of thedog; see Foramina Contents and Homologybelow). This dorsally directed foramen islocated directly ventral to p1. The lingualsurface of the body is smooth. The thicknessof the body decreases gradually toward therounded ventral border, which is roughlystraight in lateral view.

The mandibular symphysis, in the parsincisiva of the body, is the median synchon-drosis (synchondrosis intermandibularis + su-tura intermandibularis) that connects the leftand right mandibular bodies and extendsfrom the anteriormost edge of the mandibleto the middle of p3 (fig. 7) with a markedslope in lateral view (fig. 6). The symphysealregion has a rostral and a caudal surface,a dorsal border that bears the alveoli of theincisors (arcus alveolaris), and a ventralborder. The rostral or mental surface isslightly convex; in anterior view, the alveolarborder has a minute notch between the innerlower incisors. The deep emargination for thecanines is also visible laterally in anteriorview. The mental surface decreases in widthventrally, accompanying the converging ca-nine roots that reach the bottom of themandibular body (fig. 8). The mental surfacebears the anterior mental foramina (fig. 8),which are smaller than the posterior foram-ina and are located immediately ventral tothe i1–i2 embrasure. The anterior mentalforamina open somewhat laterally and dor-sally. The caudal symphyseal surface isnarrowly concave and smooth, with somefour small nutrient foramina alongside theintermandibular contact. In the caudal sur-face, the alveolar line (arcus alveolaris) iscontinuous and the alveoli for the canine andthe incisors are coalescent; that is, the bonywall that divides the space between the teethis incomplete in the middle. The caudoventralmargin of the symphyseal region serves forthe attachment of the m. genioglossus, whichdraws the hyoid apparatus rostrally whencontracted (Griffiths, 1982). In that area,a central knob, visible also in lateral view, is

Fig. 19. Pteropus tonganus USNM 546610,dorsal (Above) and oblique rostrodorsolateral(Below) views of the hyoid apparatus and theattached thyroid cartilage. Scale 5 1 mm. Abbre-viations: bahy basihyoid; ccthy caudal cornu ofthyroid; cehy ceratohyoid; ephy epihyoid; lthylamina of thyroid; rcthy rostral cornu of thyroid;sthy stylohyoid; thhy thyrohyoid; thhya thyrohyoidarticulation; thy thyroid cartilage; thyfi thyroidfissure.


flanked by two pits caudoventral to thecanine roots. Three irregularly distributed,minute nutrient foramina are present in thecaudoventral margin.

The ramus is a thin plate of bone thatcomprises roughly the caudal third of themandible (fig. 6). It has two processes—thecoronoid process (processus coronoideus) andthe mandibular condyle or articular process(processus condylaris). The angle of themandible (angulus mandibulae) lacks a true,salient angular process (processus angularis).The coronoid process is directed dorsally andslightly outwardly. Its dorsal border isa continuation of the alveolar line, whichrises at a ca. 45 degree angle, starting froma short distance behind m3. The maximumheight of the coronoid process is roughlyequivalent to the height of the canine. The m.temporalis inserts on the anterodorsal borderof the coronoid process. From the curveddorsalmost area, the posterior border of thecoronoid terminates in a caudal point anda pronounced mandibular (or lunar) notch(incisura mandibulae).

The ventral border of the mandibularnotch connects posteriorly with the mandib-ular condyle, a transverse bar located at thelevel of the alveolar line (or slightly above thealveolar line in CM 87973). The outline of theconvex articular surface is oval and facesdorsocaudally. The surface itself is porousand shows the scar of a ligament attachment(the lateral ligament, lig. lateralis). The angleis comparatively inconspicuous, forming therounded caudoventral border of the ramus.Based on Pteropus tonganus (Storch, 1968),its posterior border serves for the insertion ofthe pars superficialis of the m. massetericus.The angle lies anterior to the mandibularcondyle, which then appears to protrudefrom the posterior border of the ramus. Thethin ventral border of the ramus is onlyslightly below the level of the ventral borderof the mandibular body. The lateral surfaceof the ramus has a smooth and shallowmasseteric fossa (fossa masseterica), which islimited anterodorsally by the coronoid crest(crista coronoidea, the anterodorsal border ofthe coronoid process) and ventrally by a lowcondyloid crest (crista condyloidea). Thecondyloid crest runs horizontally from theposterior end of m3 to the mandibular

condyle below the level of the alveolar line.The masseteric fossa as a whole serves for theattachment of the m. massetericus and m.zygomaticomandibularis. Based on Rousettusaegyptiacus (Storch, 1968), the m. zygomati-comandibularis inserts on the condyloidcrest. Based on R. aegyptiacus and P.tonganus (Storch, 1968), the m. massetericus(both its pars superficialis et profunda) insertson the inconspicuous masseteric line, thecrest that accompanies the outline of theangular process. The smooth medial surfaceof the ramus is divided into two areas (whichcorrespond to the areas on the lateralsurface) by a low crest that is the medialcounterpart of the lateral condylar crest.Immediately ventral to the crest in the middleof the ramus is the posteriorly directedmandibular foramen. A large sulcus ema-nates from the foramen caudally. The man-dibular canal (canalis mandibulae) can be seenthrough the relatively transparent bone fromthe mandibular foramen to the level of thep3–p4 embrasure, running nearly parallel andclose to the ventral border of the mandibularbody. The m. temporalis (pars profunda andsuperficialis) and m. pterygoideus medialisand lateralis insert on the medial side of theramus (Storch, 1968). Based on the fetus, them. pterygoideus lateralis inserts onto themedial aspect of the mandibular condyleimmediately below the articular surface(fig. 32). On CM 87973, this attachment areais not clearly delimited from the surroundingbone, although there is some rugosity justbelow the lip of the articular surface. Theinsertion of the m. pterygoideus medialis ison the mandibular angle, again with no cleardelimitation of the attachment region visibleon the bone of the mandible. It should benoted that the inferior alveolar nerve andvessels reach the mandibular foramen bytraveling between the m. pterygoideus med-ialis and m. pterygoideus lateralis (fig. 32).

POSTERIOR BRANCHIAL SKELETON

HYOID APPARATUS

The tongue and the larynx are suspendedfrom the skull by the hyoid apparatus(apparatus hyoideus), a derivative of thesecond and partially the third pharyngeal


arches (arcus pharyngeus secundus et tertius;Nomina Embriologica Veterinaria, 1994[hereafter NEV]). In general aspect (fig. 19),the hyoid apparatus is formed by a shorttransverse bar from which two long, hornlikestructures arise bilaterally, one roughly dor-socaudolateral in position, whose proximalend attaches to skull in the ear region (theanterior cornu or hyoid arch), and onecaudolateral, which articulates with thelaryngeal cartilages (the posterior cornu,formed by a single element, the thyrohyoid,which is derived from the third branchialarch). Specifically, the hyoid apparatus iscomposed of six elements: the single basi-hyoid (basihyoideum) and the paired thyro-hyoid (thyrohyoideum), ceratohyoid (cerato-hyoideum), epihyoid (epihyoideum), stylo-hyoid (stylohyoideum), and tympanohyoid(tympanohyoideum). In Megachiroptera, thebasihyoid is fused to the thyrohyoids, and thestylohyoid is not ossified proximally so itdoes not contact the tympanohyoid (tympa-nohyal); the remaining elements are allossified and are connected by minute syno-vial joints (Sprague, 1943). These joints mayfuse in adults of some forms, except the jointbetween the basi- and ceratohyoid, whichgenerally remains a synovium in megachir-opterans (Sprague, 1943).

Based on Rousettus (Jurgens, 1963), thebasihyoid and thyrohyoids are continuousalready in the embryo. The basihyoid com-ponent of this unit is an ossification of thebasihyoid cartilage (cartilago basihyoidea,a composite originated in the pars ventralisof both the second and third branchialarches). It is a transverse bar that widenslaterally toward the articulation with theceratohyoid (see fig. 19 and below). Thebasihyoid is roughly cylindrical in shape,slightly bowed, and depressed dorsoventrally.The basihyoid contacts the ceratohyoidthrough an elliptical synchondrosis locatedin the rostrolateral angle of the basihyoid.The thyrohyoid (also termed cornu branchiale[Jurgens, 1963] and cornu majus [NAV]) is anossification of the thyrohyoid cartilage (car-tilago thyrohyoidea) of the pars ventralis ofthe third branchial arch (first branchial archin Sprague’s [1943] terminology). The thyr-ohyoids project caudolaterally from thebasihyoid as slender elements twice as long

as the transverse dimension of the basihyoid.In dorsal view, the thyrohyoids significantlydiverge caudally; in lateral view, they forma pronounced inverted arch with almostperfect curvature. Each thyrohyoid is later-ally compressed, and its caudal half formsa flange that is slightly deflected laterally.The rounded distal end of the thyrohyoid isthe hyoid component of the thyrohyoidarticulation (articulatio thyrohyoidea). InUSNM 566608, a cap of cartilage is presentin the proximal end (i.e., the end opposite tothe basihyoid).

The ceratohyoid (also termed cornu minusin the NAV) is an ossification of theceratohyoid cartilage (cartilago ceratohyoi-dea) of the pars ventralis of the secondbranchial arch (hyoid arch of Sprague[1943] and Jurgens [1963]). It is a short andflat piece that links the basihyoid with theproximal elements that suspend the hyoidapparatus from the skull (fig. 19). Theceratohyoid exhibits an apparent bending,because the major axes of its two ellipticalsynchondroses in the opposite ends of thebone are oriented differently: the distalsynchondrosis (connecting with the basi-hyoid) faces medially, whereas the proximal

Fig. 20. Pteropus tonganus USNM 546610,oblique caudodorsolateral view of the cricoidcartilage. Scale 5 1 mm. Abbreviations: crarracricoarytenoid articulation; dlcr dorsal lamina ofcricoid; mccr median crest of cricoid; thcrathyrocricoid articulation; vlacr ventrolateral arcof cricoid.


synchondrosis (connecting with the epihyoid)faces caudodorsally. The ventrolateral angleis free, wide, and rounded. There existsa fundamental difference with respect to theceratohyoid of the dog, as illustrated byEvans (1993: figs. 4–40, 4–41). In the dog, theproximal end of the ceratohyoid is directedalmost cranially and meets the epihyoid ata right angle. In Pteropus, the ceratohyoid isaligned with the epihyoid and stylohyoid inthe dorsocaudolateral direction.

The epihyoid is an ossification of theepihyoid cartilage (cartilago epihyoidea) ofthe pars dorsalis of the second branchial arch(Reichert’s cartilage). It is a simple, slenderrod that contacts the ceratohyoid distally andthe stylohyoid proximally (fig. 19). Its sectionis roughly circular, although a slight ventralridge is present. The epihyoid exhibits anapparent torsion, because the oval-shapedsynchondroses are oriented differently: themajor axis of the distal synchondrosis ishorizontal, whereas its counterpart in theproximal synchondrosis is vertical.

The stylohyoid is an ossification of thestylohyoid cartilage (cartilago stylohyoidea)of the pars dorsalis of the second branchialarch. It is incompletely ossified in Megachir-optera, as is also the case in our specimens.The stylohyoid is a laterally compressed,short bar that shows an unreduced synchon-drosis in its distal end, and a free proximalend (fig. 19). Thus, the bony contact with thetympanohyoid is lost, as in all megachirop-terans—the discreto-cornuate condition ofSprague (1963), as opposed to the integro-cornuate condition found in Microchiroptera(and many other mammals), in which allelements of the anterior cornu are ossifiedand the stylohyoid articulates with thetympanohyoid. In Rousettus, the tympano-styloid ligament connects the tympanohyoidand the stylohyoid (Jurgens, 1963; Sprague,1943), but such a ligament was not found inPteropus (Sprague, 1943). The structure andlocation of the tympanohyoid have beendescribed in the tympanic view of thepetrosal, because this element remains at-tached (and may be fused) to the cristaparotica in many specimens. The tympano-hyoid forms a joint with the petrosal(articulatio temporohyoidea), which serves tosuspend the hyoid apparatus and larynx from

the skull in forms in which the proximalanterior cornu is completely ossified (e.g.,microchiropterans).

In our limited sample, there is no obviousdifference between species and sexes in thestructure and relative size of elements inthe hyoid apparatus of Pteropus tonganus(USNM 566608, subadult female, andUSNM 566610, subadult male) and Pteropusdasymallus (FMNH 14052, adult female, andFMNH 140650, adult male). The hyoidapparatus is structurally similar but largerand markedly more robust in Pteropusgiganteus (FMNH 57661, adult female). Anadditional difference found in P. giganteus isthe presence of a tubercle in the ventralmostpoint of the arch of the thyrohyoid, probablyan attachment point of at least the m.thyrohyoideus.

LARYNX

The four component elements of thelarynx are the single epiglottic cartilage(cartilago epiglottica, missing in our speci-mens), thyroid cartilage (cartilago thyroidea),and cricoid cartilage (cartilago cricoidea) andthe paired arytenoid cartilage (cartilagoarytenoidea). These cartilages belong to thepartes ventrales of the last three branchialarches (arcus pharyngeus quartus, quintus, etsextus; NEV). The basihyoid + thyrohyoid,and the thyroid and cricoid cartilages forma telescopic arrangement of movable pieces,each of which fits within the space of the nextand therefore reduces the diameter of thelaryngeal orifice caudally (see Jurgens, 1963:fig. 13). In USNM 566608, the inner distancebetween the caudal ends of the left and rightthyrohyoids is 7.4 mm; the inner distancebetween the left and right caudal cornua (seebelow) of the thyroid cartilage is 3.7 mm; andfinally the minor (horizontal) axis of theinner ring of the cricoid cartilage is 2.9 mm.The thyroid and cricoid elements, as well asthe tracheal rings, are ossified in adultPteropus (Sprague, 1943).

The thyroid is a trough-shaped structurethat fits within the space between thethyrohyoids and articulates with them crani-ally (fig. 19). The thyroid is formed by rightand left laminae (lamina dextra et sinistra)united ventrally (fig. 19). Dorsally, the


lamina projects the rostral and caudal cornua(cornu rostralis et caudalis). The thin rostralcornu is the thyroid component of thethyrohyoid articulation, and it is noticeablyexpanded toward the joint (cranially). Anample rostral thyroid notch (incisura thyroi-dea rostralis) excavates ventral to the cornuat the expense of the cranial edge of thelamina. The caudal cornu is comparativelyshorter and less expanded distally. A corre-spondingly less pronounced caudal thyroidnotch (incisura thyroidea caudalis) is presentin the caudal margin of the lamina. The endof the caudal cornu is the thyroid componentof the cricothyroid articulation (articulatiocricothyroidea). In dorsal view, the dorsalmargin of the laminae diverges cranially tomeet the thyrohyoids. In lateral view, thelaminae slightly reduce their width ventrally.The middle part where the laminae meet isprojected cranially and approximately fol-lows the curvature of the caudomedialmargin of the basihyoid + thyrohyoid (in itspostmortem position, the thyroid and thebasihyoid + thyrohyoids are separated byapproximately 1 mm). In the dog, the cra-nioventral and caudoventral margins of thethyroid exhibit a laryngeal prominence (pro-minentia laryngea) and a thyroid fissure(fissura thyroidea), respectively. In our Pter-opus specimens, the former is absent, buta conspicuous thyroid fissure is present(fig. 19). Both the medial and lateral surfacesof the laminae are smooth.

The cricoid is a complete ring that fitswithin the space between the thyroid laminae;it is formed by a dorsal lamina (laminacartilaginis cricoideae) and a ventrolateralarch (arcus cartilaginis cricoideae; fig. 20).The lamina is about 5 mm long, with caudaland lateral margins chiefly straight andparallel, and a triangular cranial margin.On the side of this triangle is the indistinctfacet of the cricoid component of thecricoarytenoid articulation (articulatio cri-coarytenoidea). The dorsal surface of thelamina is divided by an irregular mediancrest (crista mediana), and the sides areinclined ventrolaterally as a two-sided roof.The cricoid component of the cricothyroidarticulation is a marked tubercle in thecaudolateral angle of the lamina. Immediate-ly cranial to it, the lateral margin of the

lamina is inflected medially and then con-tinues cranially in the lateral crest, whichneatly separates the lamina from the arch.The latter is ventrally no wider than 1 mm. Inlateral view, the caudal margin of the arch isroughly vertical, so the cranial edge of thearch is comparatively much longer than thecaudal margin, and reaches the cranial edgeof the lamina describing a gentle sigmoid line.The cranial margin of the arch is slightlyenlarged as a lip. The arch is significantlythinner and becomes translucent in its lateralsurface. The caudal margin of the archconnects via ligaments to the first trachealring.

The paired arytenoid cartilage is a smallelement confined to the articular area of thecraniolateral facet of the cricoid lamina, inthe craniodorsal region of the cricoid. Thearytenoid cartilage of Pteropus is greatlysimplified in comparison with the cartilageof the dog. In Pteropus, it exhibits threedelicate processes that emerge from a poorlydefined body and are oriented in differentdirections. The process located dorsally is thelongest and thinnest, and is craniocaudallycompressed, and its dorsal end forms the first(dorsomedial) of two points of contact of thearytenoid cartilage with the cricoid. Theother two processes are similar in shape,much shorter than the dorsal, each taperingto a round point. The ventrocaudal process isthe second contact with the cricoid. Thecranioventral process is free. The wholearytenoid cartilage is curved such that itfollows the outline of the laryngeal orifice.

INTERNAL SURFACES OF THE SKULL

NASAL SURFACE

The facies interna of the nasal is the roof ofthe nasal meatuses. It is a featureless surface,slightly concave, with subparallel marginsthat are slightly curved ventrally. The ventralview of the nasal generally follows theexternal shape of the bone; that is, it hasa straight medial border and a gently bowedlateral border. The caudal portion of thebone, which is not entirely visible externallybecause it is overlapped dorsally by themaxilla in the nasomaxillary suture, overlapsin turn the frontal in the frontonasal suture,


expanding laterally into a triangular wedge ofvery thin bone.

Additionally, the isolated nasal preservesthe internal surfaces of two squamoussutures, the nasoincisive and nasomaxillarysutures, and one thin plane suture, theinternasal suture. The first two sutures arecoalesced anteriorly in the nasal. The surfaceof overlap forms a lateral shelf on the nasalseparated from the externally visible medialpart by a sharp longitudinal line, correspond-ing to the external outline of the two sutures.The internal surface of the internasal sutureforms a low, slightly rugose ridge—the septalprocess (processus septalis)—of constant sizethroughout the anterior four-fifths of thenasal length. There is no nasoethmoidal crestor fossa, because the nasal does not contactthe ethmoid.

PREMAXILLARY SURFACE

The internal surface of the premaxilla isgently concave and generally smooth. Thecaudal edge of the premaxilla corresponds tothe premaxillary part of the maxilloincisivesuture. The maxilla overlaps the premaxillain the ventral half of this suture, and theopposite is true for the dorsal part. In theventral part, the suture exhibits a low ridgecaudally and a shallow groove laterally. Thesurface of the groove is rugose and ispenetrated by two alveolar foramina thatconnect directly with the large and conicalalveoli of the two upper incisors (see alveolarcanal below). The foramina are close togetherin the dorsal portion of the groove, with thedorsal foramen larger than the ventralforamen. The former supplies the alveolusof I1 and the latter the alveolus of I2. Theopenings of the alveoli are subequal in size,circular in outline, and separated by a thinbut firm wall of bone. The depth of thealveoli can be determined from externalexamination because the bone is very thin.The alveolus of I1 extends half the length ofthe entire premaxilla, whereas the alveolus ofI2 does not surpass a third of that length. Apair of very subtle juga is observable inassociation with the alveoli on the internalsurface of the premaxilla. Ventrally on theinternal surface, a small depression is presentin the space between the two alveoli. The

internal surface of the intermaxillary suture isroughly rectangular, higher than wide, pre-senting a slightly rugose surface.

The dorsal part of the maxilloincisivesuture is suggested, in the premaxilla, bya change in coloration of bone in the overlaparea (but see the maxillary counterpartbelow). In the nasoincisive suture, the nasalis laterally overlapped by the premaxilla, butthe extension of this overlap is very limited; itshows as a very subtle thinning of the dorsalmargin of the premaxilla.

MAXILLARY SURFACES

In Pteropus livingstonii AMNH 274466,the ventral nasal concha is firmly attached tothe medial surface of the maxilla, precludingexamination of some structures in medialview. The ventral nasal concha was missingfrom P. livingstonii AMNH 274515, thusexposing the medial surface of the maxilla.Both specimens were used for the descriptionof this region (fig. 21A, B).

The facies nasalis of the maxilla is essen-tially a medial concave surface with onetransverse shelf, the palatine process. Thelatter meets the medial surface of themaxillary body, a medially inclined wall towhich the ventral nasal concha attachesmedially through a long conchal crest (cristaconchalis). The internal surfaces of the rightand left maxillae contain the nasal meatuses,and the ventral nasal concha divides the nasalmeatus into three distinct spaces. Thesedivisions are the common nasal meatus(meatus nasi communis), medial to the con-chal lamina, the dorsal nasal meatus (meatusnasi dorsalis), dorsal to the conchal crest(further separated by the rostral process ofthe ethmoturbinal from another space ventralto it, the middle nasal meatus or meatus nasimedius), and the ventral nasal meatus (meatusnasi ventralis), ventral to the conchal crest.The most conspicuous features of the faciesnasalis (see details below) include the naso-lacrimal canal, the alveolar canal, the internaljugum of the canine, and the wide dorsallamina that is part of the squamous sutureswith the nasal, lacrimal, and frontal.

In the midsagittal plane, two sutures arepresent: the plane intermaxillary suture and,dorsal to it, the vomeromaxillary suture


(sutura vomeromaxillaris). The latter runsalong the entire length of the intermaxillarysuture, decreasing its dorsal developmentcaudally. The dorsal surface of the palatineprocess is horizontal, generally smooth, andmeets the maxillary body laterally in a gentlyconcave surface that rolls to meet the conchalcrest dorsally. A tiny foramen is presentbilaterally in this surface at the level of theposterior root of P4, 1 mm lateral to themidsagittal plane. The concave caudal edgeof the palatine surface is notched for theopening of the major palatine foramen.

The conchal crest extends from the rostraledge of the maxilla to approximately the levelof the anterior root of P4. In medial view, thecrest is gently convex dorsally and protrudesmedially ca. 1 mm. The alveolar canal(incisivomaxillary canal of the dog, canalismaxilloincisivus) runs immediately dorsal tothe crest in the substance of the maxilla. Thiscanal supplies the alveoli of the premolars,the canine, and finally the incisors (unlike thedog, the alveolar canal also supplies the rootof P4 in Pteropus). It opens caudally ina small, round foramen located medial to themaxillary foramen, just above the anterior(dorsally open) root of M1 (fig. 12). In oursample, the alveoli of the two roots of P3 andthe single root of the canine are perforated bymultiple alveolar foramina, whereas thealveoli of each of the two roots of P4, M1,and M2 open through a single foramen. Thecourse of the alveolar canal is visibleexternally in several specimens of P. lylei,particularly AMNH 237595 (see fig. 39). Inthis specimen, the alveolar canal followsa curved rostrodorsal path, caudally convex,from the anterior M1 root medial to theinfraorbital canal to near the canine root.This latter point is horizontally at the level ofthe lacrimal foramen and vertically at thelevel of the anterior root of P3.

One very conspicuous feature of the faciesnasalis is the nasolacrimal canal (canalislacrimalis). Preceded caudally by a widesulcus lacrimalis, the nasolacrimal canalopens caudally at the level of the posteriorroot of P3, and slightly ventral to the middleof the facies nasalis dorsal to the conchalcrest (fig. 21B). The opening itself is ratherirregular and leads to an oblique intramax-illary course that crosses the conchal crest.

The nasolacrimal canal opens in the ventralnasal meatus at the level of the P1–P3embrasure. The course of the nasolacrimalcanal is marked as a subtle relief in the faciesnasalis. More conspicuous, the internal ca-nine jugum is visible on the facies nasalisboth dorsal and ventral to the conchal crest.

The dorsal margin of the maxilla isdominated by the wide nasomaxillary suture(fig. 21). The thin lamina by which themaxilla overlaps the lateral margin of thenasal increases its dorsal extension caudallyto form the frontal process of the maxilla(processus frontalis), the maxillary compo-nent of the frontomaxillary suture. Thisprocess, which in the intact skulls liesbetween the caudolateral angle of the nasaland the lacrimal, is truncated caudally andleads ventrally to the wide, concave notchinto which the lacrimal fits. Following thisnotch to its caudal end and immediatelydorsal to the infraorbital canal is a triangularplatform on which the lacrimal rests. Justmedial and ventral to this platform for thelacrimal, as well as medial to the infraorbitaland alveolar canals, is a thin and irregularsheet of bone that is the maxillary part of theethmoidomaxillary suture (sutura ethmoido-maxillaris).

The rostral margin of the maxilla isentirely occupied by the maxilloincisivesuture. The premaxilla fits in the deeplyincised maxillary margin and is overlappedby the maxilla both medially and laterally.The rostral opening of the alveolar canal is inthe middle of the suture and appears asa faint, ventrally directed sulcus. This canaldivides within the substance of the maxilloin-cisive suture, appearing as a double canal (thedivision leading to each of the two incisoralveoli) on the premaxillary surface of thesuture. The caudal edge of the facies nasalis isdeeply concave, forming the perpendicularportion of the palatomaxillary suture.

The ventral nasal concha is an elongatedvertical lamina of porous bone attachedlaterally to the conchal crest (fig. 21A; seealso fig. 4). The shape of the concha iscomplex, but it can be described basically asa lamina from which four short folds arise.One fold is in the dorsal edge, as it scrollslaterally and then ventrally. The fold of theventral edge is double, with one lamina


projecting laterally and dorsally, and anotherlamina projecting medially and then dorsally.The last fold arises from the middle of theconcha on the medial side, and scrollsventrally, leaving a deep excavation in theventral part of the concha. In medial view,

the concha is cigar-shaped. The rostral edgeis triangular, with a vertex pointing rostrally.The ventral edge is slightly convex, and itfolds laterally and dorsally in the caudal two-thirds of the conchal length. The dorsal edgepresents a conspicuous concavity in the

Fig. 21. Pteropus livingstonii, medial view of the internal surface (facies interna) of the disarticulatedright maxilla of AMNH 274466 with the ventral nasal concha (vnc) in place (A), and the disarticulatedright maxilla of AMNH 274515 with the ventral nasal concha removed (B). Arrow labeled a indicates thecaudal opening of the infraorbital canal (not visible). Arrows labeled nalacc indicate the caudal and rostralopenings of the intramaxillary course of the nasolacrimal canal. Abbreviations: ccr conchal crest ofmaxilla; frp frontal process of maxilla; im infraorbital margin; M2 second upper molar; mdnm middledorsal nasal meatus; mxtu maxillary tuberosity; nalacc nasolacrimal canal; palp palatine process of maxilla;ptpmx pterygoid process of maxilla; snamx sutura nasomaxillaris; vnc ventral nasal concha; vnm ventralnasal meatus; zpmx zygomatic process of maxilla.


rostral third. From the rostral edge of thisconcavity, a groove arises and crosses themedial surface obliquely in a caudoventraldirection to the middle of the concha. Thesurface dorsal and caudal to this groove isflat and more lateral than the surface rostraland ventral to this groove. In this dorsalrecess fits the rostral process of the ethmo-turbinal, which lies caudal, medial, andslightly dorsal to the ventral nasal concha.After the mentioned concavity, the dorsalmargin of the ventral nasal concha is convex,then it descends gently throughout the caudalextension of the concha to meet the caudalend of the bone at the level of the ventralmargin. A deep, longitudinal groove exca-vates the medial surface of the conchabetween the scroll of the ventral margin andthe midline, approximately at the level of thelateral attachment to the conchal crest. Thedorsal edge of that groove forms the medialmidline fold, whose border is altered bya continuation of the oblique groove for thedorsal concha in the form of a ventral tip.The caudal end of the ventral nasal conchaexhibits a distinct caudolateral flange. Thelateral view of the ventral nasal concha is notavailable to direct examination, but it can beinferred from the presence of the conchalcrest and the development of the dorsal andventral folds.

PALATINE SURFACE

In the isolated palatine bone, the surfacesof the nasopharyngeal meatus (facies nasalis)and the large, squamous frontopalatinesuture in the perpendicular process are themost salient internal features (fig. 22). Theleft and right portions of the nasopharyngealmeatus, each contained in an individualpalatine bone, are each oval in outline withthe medial side open and communicatingwith the corresponding portion in the otherpalatine. Medially and ventrally, the naso-pharyngeal meatus is bounded by the nasalcrest, which decreases in height rostrally. Thearticular surface of the nasal crest, orinterpalatine suture, is very rugose. Mediallyand dorsally, the meatus is bounded by thethin sphenoethmoid lamina (lamina sphe-noethmoidalis). Anteriorly, this lamina formsa medial flange partially roofing the meatus,

decreasing its width rostrally. The meatusitself is a smooth tube that gradually funnelscaudally into the choanae. Near the rostralend of the palatine is the opening of thesphenopalatine foramen. The crescent-shaped space between the sphenopalatineforamen and the rostral edge of the palatineis the palatine contribution to the maxillaryrecess (recessus maxillaris). The recess islimited ventrally by the ethmoidal crest(crista ethmoidalis), a low, rostrally concaveridge connecting the sphenopalatine foramenwith the rostroventral angle of the nasopha-ryngeal meatus. One (left side) or two (rightside) extra, smaller openings of the spheno-palatine foramen are present caudal to themain foramen in AMNH 274466 (all of themopen to the lateral side of the perpendicularlamina; cf. CM 87972, 87973). Dorsal to thesphenoethmoid lamina, and oriented ata right angle to it, is the palatine contributionto the frontopalatine suture. Through thisthin lamina, the palatine overlaps the parsorbitalis of the frontal bone in the frontopa-latine suture laterally and also contacts theethmoid medially in the palatoethmoidalsuture (sutura palatoethmoidalis). Conse-quently, the frontal and ethmoid fit in thespace between the sphenoethmoid laminaand the dorsal portion of the perpendicularlamina, unlike the dog, in which the contactis with the vomer and not with the ethmoid.This difference results from the reducedwings of the vomer in Pteropus (see below).

The rostral end of the palatine, not visibleexternally, is truncated and formed by thevery thin bone of the squamous palatomax-illary suture (fig. 22). Here the palatine isoverlapped widely by the maxilla laterally.The rostral external surface of the isolatedpalatine shows a deep wedge accommodatingtwo connected parts of the maxilla: thecaudal part of the palatine process of themaxilla medial to the maxillary tuberosity,and the pterygoid process of the maxilla. Justmedial to this area, on the ventral side, is theexposed course of the palatine canal, whichopens through the major palatine foramen inthe palatine side of the palatomaxillarysuture.

The caudal sphenoidal process (processussphenoidalis) contributes to the ectopterygoidprocess (fig. 10). The sphenoidal process


shows two deep concavities where the othertwo components of the ectopterygoid processfit: dorsolaterally is a larger, teardrop-shapedsurface for the articulation of the alisphenoidcontribution to the ectopterygoid process,and ventromedially is a smaller surface forthe articulation of the pterygoid. The twosurfaces are separated caudally by a thin andsharp lamina of bone.

FRONTO-ETHMOIDAL SURFACES

The frontal, ethmoid, and vomer aresolidly fused in the disarticulated specimensof Pteropus livingstonii available for exami-nation (figs. 23, 24A, B). Based on AMNH274466, two distinct internal surfaces can bedistinguished. One surface is dorsocaudal,comprising the inner table of the frontal(facies interna) and the cribriform plate of theethmoid (lamina cribrosa; fig. 23). The othersurface (fig. 24) is ventrolateral and rostral,comprising the ventral surface of the vomer,the rostroventral and partially lateral sur-faces of the ethmoid (pleurethmoid of Jur-gens, 1963), and the rostral process of theethmoturbinal (anterior tip of ethmoturbinalof Jurgens, 1963).

The facies interna of the frontal roofs therostral cranial fossa (fossa cranii rostralis)and provides the dorsal and lateral (orbital)walls of the ethmoidal fossae (fossae ethmoi-dales), the space immediately posterodorsalto the cribriform plate (fig. 23). The faciesinterna of the frontal is a cup-shaped surface.A faint trace of cerebral juga corresponds tothe bilateral mark left by the longitudinalfissure of the brain, which is reproduced inthe facies interna as two rostrally divergentcurved lines, separated caudally by 1 mm androstrally by ca. 4 mm. The circular border ofthe postorbital area of the frontal bone israther irregular. In dorsal view, the extent ofthe parietal overlap, through its wedge-shaped frontal process of the parietal, be-comes evident in the disarticulated skull. Theexposed forehead is limited to the medianrectangular space marked bilaterally bya groove parallel to the sagittal plane at thelevel of the postorbital foramen. The caudalmargin shows a frontoparietal suture that ispart plane and part squamous. In the mid-sagittal line, a wedge-shaped medial process

of the caudal margin of the frontal fits intoa complementary recess of the rostral borderof the parietal (the plane segment of thefrontoparietal suture). Lateral to this suture,the frontal slightly overlaps the parietal viaa bilateral wedge-shaped process of its caudalborder (the squamous segment of the fronto-parietal suture).

Rostral to the rostral cranial fossa are thebilateral ethmoidal fossae, each containingan olfactory bulb (bulbus olfactorius). Incaudal view (fig. 23), the fossae form anample space, twice as high as wide, withrounded corners and slightly narrower ven-trally. This space is ill-defined as twochambers, corresponding to each ethmoidalfossa, with the division marked by a crest inthe dorsal wall (contributed by the frontal)and by a low crista galli in the rostral wall,the cribriform plate of the ethmoid (laminacribrosa). The thin and low crista galli is thedorsalmost part of the perpendicular laminaof the ethmoid (lamina perpendicularis),which forms the osseous nasal septum(septum nasi osseum). The cribriform plate isinclined so that the dorsal edge is rostral withrespect to the ventral edge. The plate exhibitsnumerous perforations, the cribriform fo-ramina (foramina laminae cribrosae), for thepassage of bundles of the olfactory nerves(nn. olfactorii). The cribriform foramina areorganized into tracts whose positions are,based on a partially damaged specimen ofPteropus livingstonii (AMNH 274515), re-lated to the attachment of turbinates on therostral side of the cribriform plate. In P.livingstonii AMNH 274466, the cribriformforamina are grouped into two columns,medial and lateral, within each ethmoidalfossa (fig. 23). The medial column consists offour irregular groups. The dorsal group is thelargest and consists of one principal perfora-tion with a bilaterally variable number ofvery small perforations, especially in thewalls of the main foramen as they sink intothe ethmoidal labyrinth (labyrinthus ethmoi-dalis). The same pattern is found in the othermain foramina of the medial column, whichare more closely associated among them-selves. In the dorsolateral angle of theethmoidal fossa is a group of two (right side)to four (left side) main foramina surroundedby some smaller perforations. Immediately


ventral to these is the lateral series ofcribriform foramina. These are grouped intofive clusters of one or two larger foraminaaccompanied by smaller perforations, locatedclose to the lateral edge of the cribriformplate. The left and right ventralmost groupsof foramina are placed closer to the cristagalli. The bone between the medial andlateral columns of foramina, as wide as oneof those columns, is perforated occasionallyand irregularly by small foramina, but it isessentially solid. The lateral walls of theethmoidal fossae are smooth, presentinga wide ethmoidal notch (the ethmoidalforamen in the articulated skull, with itscaudal concavity closed by the orbitosphe-noid). Finally, the dorsal aspect of theethmoidal fossae is biconcave, formed bytwo elongated domes separated by thelow frontal crest (crista frontalis). Themorphology of the cribriform plate ofP. livingstonii (this study, fig. 23) is verysimilar in every respect to the morphologyreported by Bhatnagar and Kallen (1974)for Pteropus giganteus (see their plate 1, fig. 8,p. 85).

The ventral surface of the frontoethmoidalcomplex includes the vomer (medially androstrally), the ventral surface of the ethmoid(lamina basalis, caudolaterally), and theventral surface of the rostral process of theethmoturbinal (laterally and rostrally;fig. 24B). In the disarticulated skull, the

vomer is fully exposed in ventral view. Aslong as half the skull length, the vomerextends from the incisive fissure to thesphenoidal sinus. Both ends (the incisiveand sphenoidal incisures) are visible exter-nally and, therefore, are described above (seeVomer). Ventrally, the vomer exhibitsa paired wing (ala vomeris) in the caudalthird of its length (only partially visibleexternally), each separated medially by a lon-gitudinal crest (crista vomeris). The wings arevery narrow, ca. 1 mm wide throughout theirlength. The suture with the ethmoid (suturavomeroethmoidalis) is almost straight andbarely visible. These alae vomeris are contin-uous caudally with the bifid ends of thesphenoidal incisure. Due to their narrowwidth, the alae form only the medial part ofthe roof of the nasopharyngeal meatusimmediately rostral to the choanae. Thelateral part of the roof is contributed by theventral surface of the ethmoid (the pleur-ethmoid of Jurgens, 1963). The ventralsurface of the ethmoid is smooth and thin,and has a roughly rhomboidal shape, withthe vomer in the midline, and four borders(two caudolateral and two rostrolateral). Thetruncated caudal edge of the ethmoid formsthe rostral edge of the sphenoidal sinus,which in ventral view appears as a pairednotch lateral to the caudal edge of the vomer.Through the rostral opening of the sphenoi-dal sinus, the nasal septum is visible. In close

Fig. 22. Pteropus livingstonii AMNH 274466, medial view of the internal surface of the palatine. Scale5 5 mm. Abbreviations: etcr ethmoidal crest of palatine; fnpa facies nasalis of palatine; mxre maxillaryrecess; ncr nasal crest of palatine; sfp sutura frontopalatina; sipal sutura interpalatina; spetl sphenoethmoidlamina; spf sphenopalatine foramen; spmx sutura palatomaxillaris; spp sphenoidal process of palatine.


examination, traces of the suture between thenasal septum (perpendicular plate, laminaperpendicularis) and the cribriform plate arevisible. The caudal view of the sphenoidalsinus, on the sides of the nasal septum, showstwo rostrocaudally elongated scrolls attacheddorsally to the ethmoid, with its ventralborder folding laterally (fig. 23). Based onRousettus (Jurgens, 1963), these are endotur-binates (or primary ethmoturbinals; endotur-binalia), specifically endoturbinate III. Thelabyrinthus ethmoidalis of Rousettus exhibitsone ectoturbinate and three endoturbinates,all of which are bilaminar, and a well-de-veloped crista semicircularis that arises fromthe tectum nasi close to the nasal septum(Jurgens, 1963). Based on a partially dam-aged specimen of Pteropus livingstonii

(AMNH 274515), we were able to prelimi-narily confirm a similar composition andconfiguration of ethmoidal elements in Pter-opus, but a detailed anatomical description ofthe labyrinth requires further study.

In the caudolateral border is the fron-toethmoidal suture, in which the dorsolateralcomponent contributed by the frontal andthe medioventral component contributed bythe ethmoid meet at an almost right angle.The frontoethmoidal suture is incomplete insealing the caudolateral border, leaving a cleftthat is larger on the right side in AMNH274466. The rostrolateral border of theethmoid exhibits a ventral process from thelateral lamina of the ethmoid and the fusedbase of the rostral process of the ethmoturb-inal medially (fig. 24).

Fig. 23. Pteropus livingstonii AMNH 274466, caudal view of the frontoethmoidal complex showing thecribriform plate. Scale 5 5 mm. Abbreviations: crga crista galli; crif cribriform foramina; end-IIIendoturbinate III; etfo ethmoidal fossa; itf inner table of frontal; nas nasal septum (mesethmoid); poppostorbital process; rcfo rostral cranial fossa; spsi sphenoidal sinus; v vomer.


The rostral process of the ethmoturbinalattaches to the rostroventral side of theethmoid and projects rostrally in the formof a ventrally open tube, presenting a medial

and a lateral wall joined dorsally, anddefining internal and external surfaces(fig. 24A, B). The rostral process of theethmoturbinal decreases in height and width

Fig. 24. Pteropus livingstonii AMNH 274466, frontoethmoidal complex in lateral view (A) and ventralview (B). Scale 5 5 mm. Abbreviations: alv ala vomeris; ‘‘c’’ column of bone on lateral side ofethmoturbinal; cv crest of vomer; ef ethmoidal foramen; ent-III endoturbinate III; eth ethmoid; ethtuethmoturbinal; fifr facies interna of frontal; fofr facies orbitalis of frontal; iiv incisura incisiva of vomer; isvincisura sphenoidalis of vomer; lv lamina of vomer; pnfr pars nasalis of frontal; pof postorbital foramen;pop postorbital process; sc sutura coronalis; sffr squama frontalis of frontal; sfl sutura frontolacrimalis;sfm sutura frontomaxillaris; sfn sutura frontonasalis.


rostrally, acquiring a roughly conical shape.The dorsal surface is domed. The medial wallis roughly vertical and is deeper than thelateral wall. The lateral wall folds its ventralmargin medially. Caudally, the lateral wallexhibits a deep incisure that is separated fromanother, more caudal incisure by a thin,vertical, zigzag column of bone (probablypart of the ectoturbinate, based on Rousettus;Jurgens, 1963). The caudalmost incisure isseparated from the ethmoid by an obliqueridge that is expanded ventrally as a shortflange. The space between this ridge and thefrontoethmoidal suture caudally has twodeep, oblique grooves. In the caudal part ofthis area is the articulation with the lacrimalin the lacrimoethmoidal suture (sutura lacri-moethmoidalis of the dog, probably equiva-lent to the sutura lacrimoconchalis of theNAV). Ventral and caudal to this part, andadjacent to the frontoethmoidal suture, is theethmoidal component of the ethmoidomax-illary suture. All the surfaces involved areformed by noticeably porous bone. Thecaudal portion of the ventral nasal conchafits inside the hollowed cone of the rostralprocess of the ethmoturbinal, and the cleftbetween both conchae is the middle nasalmeatus.

PRESPHENOID SURFACE

In the dorsal surface of the presphenoid-orbitosphenoid complex (fig. 25A), the mostsalient features are the large alae orbitales(orbitosphenoid), the long corpus (presphe-noid), the yoke (jugum sphenoidale), and theoptic canals (canales optici). The presphenoidbody has two shallow optic grooves, eachleading to their respective optic canals,separated by a medial, low, and roundedmidsagittal crest, and demarcated laterally bya low ridge at the union of the alae with thecorpus caudal to the optic canals. The alaeare fused seamlessly to the corpus. Lateral tothe corpus is the paired, spine-shaped, verysmall rostral clinoid process (processus clin-oideus rostralis). Laterally, the alae connectsmoothly to the body and, bridging over theoptic canals, connect themselves again dorsalto the corpus. The outline of each optic canalis somewhat oval, with the dorsal orbito-sphenoidal crest (crista orbitosphenoidalis)

forming the flattened dorsal margin. Theyoke, the rostral union of the left and rightalae, is dorsally gently concave. The alae arevery wide and emerge from almost the entireside of the long corpus. The alae first spreadwidely laterally, more so caudally, and thenthey gently curve dorsally, keeping a roughlyuniform width until reaching the roundeddorsal margin. The caudal alar margin showsa distinct notch representing the rostralmargin of the sphenorbital fissure, caudaland lateral to the optic canals. The elevated,roughly vertical part of the alae is orientedobliquely with respect to the midsagittalplane, converging rostrally. The anteriorinteralar space, where the caudal frontoeth-moidal complex fits, is U-shaped in caudalview. Externally, the alae show the wideoverlap of the orbitosphenoid’s portion ofthe squamous sphenoparietal suture alongthe posterior third of the external surface.The corpus itself has truncated anterior andposterior ends. The anterior end shows thevery small, paired cavity that the presphenoidcontributes to the sphenoidal sinus (aperturasinus sphenoidalis). Ventral and slightly cau-dal to the sphenoidal sinuses, there is a thirdmedian cavity that probably houses a rod ofcartilage (lost) connecting the presphenoidwith the vomer and nasal septum rostrally.The caudal end has a mushroom-shapedsection and is also in contact with a rod ofcartilage (lost in most macerated specimens,but present, for instance, in Pteropus gigan-teus ROM 75747 and Dobsonia pannietensisAMNH 159099) linking the presphenoid andbasisphenoid.

BASISPHENOID SURFACE

The dorsal aspect of the basisphenoid-alisphenoid exhibits two large temporal alae(the alisphenoid component) united by a trun-cated pyramidal corpus (the basisphenoidcomponent; fig. 25B). On each side of thetruncated rostral end of the corpus is theshort, spinelike pterygoid process (of thebasisphenoid). The outline of the rostralend is dorsally convex, with two lateral sidesconverging in the ventral midline, with allangles rounded. The dorsal surface of thecorpus has a large central depression, thesella turcica, with its hypophyseal fossa (fossa


hypophysialis) flooring the hypophysis in life.The fossa is oval in shape, longer than wide,with its surface very smooth, bounded bi-laterally by low, rounded ridges, and caudallyby a thicker ridge, which represents a weakdorsum sellae. Caudally, the corpus presentsa rather flat, lip-shaped articular surface forthe cartilage of the spheno-occipital synch-ondrosis (lost). Lateral to this synchondrosisis the shallow carotid sulcus (sulcus caroti-cus), which transmits the contents of thecarotid foramen to the sella turcica. Themedial border of the carotid sulcus projectscaudally as a short spine. Immediately lateralto the sulcus is a low ridge that coincidestopographically with the lingula sphenoidalisof the dog and human.

The dorsal surface of the alae (faciescerebralis) is large, roughly triangular inshape, with a rostral vertex and a caudome-dial base. The surface is gently concave,presenting principally two notches, medialand lateral, in the rostral edge immediatelylateral to the corpus, and a large foramenovale in the substance of the ala. The lateralnotch forms the caudal edge of the sphenor-bital fissure, and projects ventrally a footlikepterygoid process that rests on top of thejunction of palatine and pterygoid, and ispart of the ectopterygoid process. The largermedial notch presents a deep wedge shape; itis floored by the rostromedial process of thepterygoid, and thus it is not visible externally.The large foramen ovale is elliptical in shapeand oriented obliquely so the major axes ofthe left and right foramina converge rostrally.This foramen, the result of the fusion of theforamen ovale and the caudal alar foramenof the dog, is in the center of the basal alarconcavity. A fairly well marked sulcusascends gently from the rostral edge of the

foramen to the sphenorbital fissure, pre-sumably transmitting the contents of theabsent alar canal. Caudolaterally, the alaforms a lobe, the epitympanic wing of thealisphenoid, which forms the rostral marginof the piriform fenestra. The epitympanicwing projects into the ear region, where itcontacts the petrosal along a serrate suture,and also the epitympanic wing of the parietal.The lateral alar border is rather irregular.The lateral side of the epytimpanic wingshows the small (ca. 1 mm wide) squamoussphenosquamosal suture, by which the squa-mosal overlaps the alisphenoid laterally, seenin ventral view. In dorsal view, this sutureshows as a short, inverse alisphenoid-squa-mosal overlap, immediately rostral to theepitympanic wing of the alisphenoid, wherethe ventral and medialmost portions of thesquamosal, in the medial angle of the glenoidfossa, contact the alisphenoid and forma partly serrated, partly squamous suture.The triangular rostral edge of the ala, indorsal view, is divided into two portions,each representing a squamous suture. Thesmaller medial portion corresponds to theunnamed suture by which the alisphenoidoverlaps the orbitosphenoid medially. Thesecond suture corresponds to the portion ofthe sphenoparietal suture by which thealisphenoid overlaps the parietal medially.

PARIETAL SURFACE

The left and right parietals, as well asthe interparietal, are articulated in AMNH274466, forming a parietal complex that istreated as a whole here (fig. 26). Deeplyconcave, the ventral surface of the parietalcomplex (facies interna of the parietal, laminainterna of the cranium) reproduces the

r

Fig. 25. Pteropus livingstonii AMNH 274466, dorsocaudal view of the internal surface of thepresphenoid-orbitosphenoid complex (A) and dorsal view of the internal surface of the basisphenoid-alisphenoid complex (B). Scale 5 5 mm. Abbreviations: ao alae orbitales of sphenoid (orbitosphenoid); asalisphenoid; asu alar sulcus of alisphenoid; at alae temporales of sphenoid (alisphenoid); bs basisphenoid;cs carotid sulcus of basisphenoid; ds dorsum sellae; ecptp ectopterygoid process; etwas epitympanic wing ofalisphenoid; fh fossa hypophysialis; fo foramen ovale; jsp yoke or jugum sphenoidale; lsp lingulasphenoidalis; opc optic canal; os orbitosphenoid; ps presphenoid; ptpbs pterygoid process of basisphenoid;rcp rostral clinoid process; sisp synchondrosis intersphenoidalis; spof sphenorbital fissure; ssposynchondrosis spheno-occipitalis; st sella turcica.


bulbous shape and some external features ofthe underlying brain. These features are thedigital impressions (impressiones digitatae),separated by intermediate ridges, whichcorrespond to the cerebral gyri and sulci,respectively.

In AMNH 274466, the plane, linear inter-parietal suture is clearly visible for most of itslength, on both dorsal and ventral surfaces,becoming indistinguishable only ca. 1 mmrostral to the contact with the parietointer-parietal suture. The latter is still visible, but itexhibits a higher degree of fusion. Againsta light source, it is possible to see that theparietointerparietal suture is largely a planesuture, with small areas of overlap (by theparietal, dorsally) only in the rostral and thelateral margins.

Rostrally, the parietal widely overlaps thefrontal in the coronal (5 frontoparietal)suture, a large triangular area of thin bonewell delimited caudally by a neat line at thelevel of the rostral edge of the parietal in themedian plane. The externally visible area ofthe sinciput fits in the rectangular spacebetween the two triangular areas of thefrontoparietal suture (fig. 1). The caudal edgeof that space (i.e., the rostral margin of theparietal in the median plane) has a V-shapedincisure in the sagittal suture.

The ventral margin of the exposed parietalis complex and presents several angles andborders, for which we propose the followingnomenclature (fig. 26B). From rostral tocaudal, the angles are the frontal (angulusfrontalis), sphenoidal (angulus sphenoidalis),epitympanic (new term), vascular (new term),and mastoid (angulus mastoideus); the mar-gins or edges are the frontal (margo frontalis,ventral part), squamous (margo squamosus),epitympanic (new term), and caudoventral(new term). The frontal angle, as describedabove, is the rostralmost extension of theparietal and forms the apex of the frontopar-ietal suture. The ventral part of the frontalmargin is straight; it is inclined ventrocaud-ally until reaching the ventralmost point inthe parietal, where it terminates at thesphenoidal angle, which marks the beginningof the sutura squamosa. The sphenoidalangle is located slightly rostral to the mid-point of the parietal complex. The squamousmargin arches dorsally, descending again to

the ventral tip of the triangular epitympanicwing of the parietal (i.e., the epitympanicangle), at about three-quarters of the parietallength. While the internal surface of theparietal lacks traces of sutures in this area,the external surface (facies externa) of thedisarticulated parietal shows the wide overlaparea of the sutura squamosa. Dorsal to thearched ventral margin, the area of the suturasquamosa extends generously over the lowerregion of the parietal’s dorsal surface, as-cending from the sphenoidal angle to a pointhigh above the epitympanic wing. The caudalmargin of the epitympanic wing, or epitym-panic margin, is roughly vertical and termi-nates at the caudoventral margin of theparietal at an almost right angle.

In the angle where the epitympanic andcaudoventral margins meet, called here thevascular angle, a complex configuration ofvascular sulci is present. Two different vesselsystems are involved, and they cross eachother in this angle. These are the capsulopar-ietal emissary vein and the posterior divisionof the ramus superior of the stapedial artery.The capsuloparietal emissary vein drains theblood from the intracranial transverse sinus,partially encapsulated in a short sulcus in theinternal surface of the parietal. The petrosalcloses the canal for the capsuloparietalemissary vein medially and caudally, whichbecomes evident with the petrosal in place(e.g., in the broken skulls of Pteropusneohibernicus AMNH 152402 and P. vam-pyrus AMNH 198691). The capsuloparietalemissary vein arrives in a space immediatelydorsal to the opening of the temporal canal(see below), between the squamosal and theparietal. This space appears as a depressionin the external surface in the vascular angle,and is especially evident in caudolateral viewin AMNH 274466. Then, the capsuloparietalemissary vein enters directly into the dorsalopening of the temporal canal in the medialside of the squamosal, exiting the skullthrough the postglenoid foramen (see below).In turn, the ramus superior follows aninverse, dorsally directed course (marked, inthe parietal, as a shallow sulcus on theepitympanic margin), reaching the space inthe angle between the caudal epitympanicedge and the caudoventral parietal margin. Inthat space, the posterior division of the ramus


superior crosses the more external side of thespace, and a conspicuous sulcus for thevessel, not visible externally, appears. Imme-diately dorsal, on the right side, the sulcusdivides into a smaller, caudal sulcus, leadingto the posterior foramen for ramus tempor-alis, and a larger, rostral sulcus, whichcontinues further dorsally, leading to theanterior foramen for ramus temporalis. Bothforamina open in the sutura squamosa, andtheir course between the squamosal and theparietal is not exposed externally. Both sulcicontinue 2–3 mm dorsally in the free dorsalsurface of the parietal. On the left side,a single, wider sulcus reaches the suturasquamosa, and a corresponding single fora-men for ramus temporalis is present.

The internal surface of the parietal revealsthe relatively small size of the sulcus for thetransverse sinus, as compared with the dog.The transverse sulcus has a strong, verticallydirected medial wall that fuses with the skullroof some 5 mm dorsal to the vascular angle.Two nutrient foramina are present bilaterallyin the sulcus. This is more clearly visible inarticulated specimens without the skull roof,such as Pteropus neohibernicus AMNH152402 and Pteropus vampyrus AMNH198691. A low sulcus for the transverse sinus,gently concave caudally, bridges the vascularangle and the midsagittal line. The left andright sulci meet at the junction of theinterparietal and parietointerparietal sutures.The rostral edge of the sulcus is more markedthan the caudal edge. Rostral to the sulci, theparietal surface is lightly marked by digitalimpressions and intermediate ridges. Thereare two main intermediate ridges of thick-ened bone. The medial intermediate ridgeruns rostrocaudally, separated from theinterparietal suture by ca. 5 mm, and extendscaudally up to half the distance between themedial rostral edge of the parietal and theridge of the transverse sulcus. The lateralintermediate ridge is somewhat divergentrostrally, but is still roughly parallel to themedial intermediate ridge and separated byca. 3 mm from it. Another, barely markedridge extends between the caudal end of thelateral intermediate ridge and the vascularangle. A somewhat blurred vascular groovefor the middle meningeal artery (sulcusarteriae meningeae mediae) and veins arises

from the ventral border (right side) and maybe from the epitympanic angle as well (leftside). The ramifications of the meningealvessels are not consistently marked bilateral-ly, being more numerous on the right side(some nine inconspicuous branches versus sixon the left side).

The caudal part of the ventral surface ofthe parietal complex comprises most of theinterparietal and the two caudolateral lobesof the parietal (fig. 26). The interparietal hasa domed ventral surface, surrounded by theparietointerparietal and occipitointerparietalsutures. The left side of the parietointerpar-ietal suture is more deeply marked than theright side. The occipital margin of theinterparietal shows three concave suturesegments. The two lateral segments are theareas by which the interparietal overlaps thesupraoccipital (see below). In turn, themedian segment shows a small squamousarea on the dorsal surface by which thesupraoccipital slightly overlaps the interpar-ietal. The caudolateral lobes of the parietalexhibit two large suture areas. The parietalcomponent of the occipitoparietal suture(which corresponds to the occipital marginof the parietal, margo occipitalis) is a flange ofpoorly consolidated bone presenting numer-ous notches and longitudinal striations. Thiswide lamina overlaps the supraoccipital dor-sally. The caudoventral margin of the parietalis occupied by an unnamed, plane suture withthe petrosal (see Petrosal) that is triangular inshape. In this area, the parietal widely over-laps the pars canalicularis of the petrosal.

SQUAMOSAL SURFACE

The squama of the squamosal laterallyoverlaps parts of the parietal, the petrosal,and the alisphenoid. The squama covers theparietal rostrodorsally, which projects itsepitympanic wing ventrally almost to thelevel of the anterior margin of the externalacoustic meatus. The squama also covers thepars canalicularis of the petrosal and thealisphenoid caudoventrally and rostroven-trally, respectively. Consequently, there isa very small brain exposure on the squamo-sal. In medial view (fig. 27), the outline of thesquama is the same as described externally(see Squamosal above).


The internal, or medial, surface of thesquamosal is concave, with a very prominentfeature: the dorsally directed opening ofthe temporal canal located in the posteriorthird of the squama. The temporal canaltransmits the capsuloparietal emissary veinfrom the transverse sinus to its exit at thepostglenoid foramen (see Parietal above, andForamina Contents and Homology below).The opening of the temporal canal issurrounded anteriorly, ventrally, and poster-iorly by acute ridges, and opens into a spacethat in turn leads dorsally to a wide sulcusfor the posterior division of the ramussuperior of the stapedial artery. Three minutenutrient foramina are found around thisspace. The posterior division of the ramussuperior passes medial to the capsuloparietalemissary vein in a dorsal direction, entersthe parietal, and divides shortly after,exiting the skull through two or three open-ings (the foramina for the rami temporales)at the sutura squamosa. Caudoventral to theopening of the temporal canal, a dorsallyconcave crest delimits the dorsal extension ofthe squamosal contribution to the fossaincudis, a cavity shared with the petrosal.The rostrodorsal semiarch of this crestis continued caudoventrally in the faintmark of the caudal part of articulationwith the petrosal. Immediately caudal to thisline is the posttympanic process of thesquamosal.

Anteriorly, the triangular rostral lamina ofthe squama shows a distinctive ridge thatmarks the sphenosquamosal suture. About1 mm dorsal is the less conspicuous suturasquamosa. The space between the twosutures is the very limited brain exposureon the squamosal (ca. 4 mm long 3 1 mmhigh).

OCCIPITAL SURFACE

In AMNH 274466, the four occipitalbones are fused into a single structurewithout traces of sutures internally or exter-nally except for the ventral intraoccipitalsynchondrosis (the joint between basioccipi-tal and exoccipital), which is representedbilaterally by no more than a 1-mm notch.As a consequence, the occipital complex istreated here as a whole. Centered on theforamen magnum, the cup-shaped complexof four bones forms a complete ring, with thebasioccipital (pars basilaris of the occipitalcomplex) protruding ventrally and rostrallyas a long rectangular plate, the exoccipitals(partes laterales) forming the short but thicklateral sides, and the supraoccipital (parssquamosa) appearing as a relatively thinlamina partially roofing the wide space dorsalto the foramen magnum (fig. 28).

Distinctly two-sided, with each side form-ing a plane gently converging medially andventrally, the dorsal surface of the basiocci-pital forms the sulcus medullae oblongatae.Rostrally, the concavity of the dorsal surfaceis accentuated (in the impressio pontina), andthe surface is subsequently elevated to reachthe dorsal border of the lip-shaped joint thatis the basioccipital component of the spheno-occipital synchondrosis. In each of therostrolateral angles, a short, oblique jointmarks the lateral continuation of the spheno-occipital synchondrosis immediately medialto the carotid foramen. Caudally there isa gap that corresponds to the basicochlearfissure; immediately caudal to that is theinconspicuous mark of the posterior basico-chlear commissure and then a notch repre-senting the remainder of the ventral intraoc-cipital synchondrosis. Caudally and medially,the basioccipital is marked by the acutely

r

Fig. 26. Pteropus livingstonii AMNH 274466, ventral view of the internal surface (facies interna) of theparietals and interparietal (A), and lateral view of the isolated parietal complex (B). Scale 5 5 mm.Abbreviations: cllo caudolateral lobe of parietal; cvma caudoventral margin of parietal; etan epitympanicangle of parietal; etma epitympanic margin of parietal; fipa facies interna of parietal; fran frontal angle ofparietal; frma frontal margin of parietal; imdi impressiones digitatae; ip interparietal; maan mastoid angleof parietal; ocma occipital margin of parietal; plpa planum parietale; sc sutura coronalis; soipa suturaoccipitointerparietalis; sopa sutura occipitoparietalis; span sphenoidal angle of parietal; spip suturaparietointerparietalis; sqma squamosal margin of parietal; srt sulci for rami temporales; ss sutura sagittalis;ssq sutura squamosa; sts sulcus for transverse sinus; va vascular angle of parietal.


concave margin of the foramen magnum, theintercondyloid notch (incisura intercondyloi-dea).

The exoccipital is the shortest componentof the occipital complex. Rostrally, it hasa dorsoventrally elongated, almost verticalarticulation with a convex surface, theexoccipital component of the occipitomastoidsuture, or the articulation between theexoccipital and the mastoid exposure of thepetrosal (the petrosal component of thesuture being deeply concave). This articula-tion has a notch in its dorsocaudal angle thatcommunicates with the minute mastoidforamen and continues rostrodorsally ina short, almost horizontal suture of ca.2 mm. This part of the suture is already inthe supraoccipital, based on Pteropus capis-tratus AMNH 194276. Ventral to the suture,horizontally oriented, is the wide gap of theconcave medial margin of the jugular fora-men. This margin shows a distinct sulcus thatcorresponds to the sulcus for the inferior

petrosal sinus (sinus petrosus ventralis) in thedog. Internally, the exoccipital has a smooth,convex surface that funnels into the foramenmagnum, whose lateral margin is widelyconcave. Midway between the suture withthe petrosal and the foramen magnum is therounded hypoglossal foramen.

The supraoccipital is a wide, concavelamina of bone overlying the cerebellum.The lateral angle, as described above, isoccupied by a notch connected to themastoid foramen (the foramen being delim-ited ventrally and internally by the mastoidexposure of the petrosal). The supraoccipitalhas two sections of different thickness aroundthe foramen magnum, the division roughlycoincident with the external nuchal crest. Theventral portion is formed by bone thatincreases its thickness toward the foramenmagnum. The dorsal margin of the foramenmagnum is, like its ventral counterpart,acutely concave. The dorsal part of thesupraoccipital has a central vermiform im-

Fig. 27. Pteropus livingstonii AMNH 274466, medial view of the internal surface of the squamosal.Scale 5 5 mm. Abbreviations: eam external acoustic meatus; fi fossa incudis (lateral wall); ptpposttympanic process of squamosal; sqa squama of squamosal; srt sulci for rami temporales; sspsq suturasphenosquamosa; ssq sutura squamosa; stz sutura temporozygomatica; tc temporal canal; zpsq zygomaticprocess of squamosal.


pression (impressio vermialis) that is delimitedbilaterally by the internal occipital crest(crista occipitalis interna). Lateral to theinternal occipital crests are the depressionsof the impresiones digitatae, which accom-modate gyri of the brain. The dorsal border

of the supraoccipital is formed by theoccipitointerparietal and occipitoparietal su-tures. In the median part of the supraoccipi-tal is the squamous occipitointerparietalsuture by which the interparietal and thesupraoccipital interlock. There are two deep

Fig. 28. Pteropus livingstonii AMNH 274466, oblique rostrolateral view of the occipital complex. Scale5 5 mm. Abbreviations: bo basioccipital; eo exoccipital; fm foramen magnum; hf hypoglossal foramen;imdi impressiones digitatae; iocr internal occipital crest; nmf notch for mastoid foramen; oc occipitalcondyle; omj occipito-mastoid joint; pcp paracondylar process; siocbl synchondrosis intraoccipitalisbasilateralis; smo sulcus medullae oblongatae; so supraoccipital; soipa sutura occipitointerparietalis; sopasutura occipitoparietalis; sspo synchondrosis spheno-occipitalis; veim vermiform impression.


notches on the sides of the vermiformimpression. These notches are the areaswhere the supraoccipital is overlapped dor-sally by the interparietal. The middle portion,immediately dorsal to the vermiform impres-sion, is the small rounded area where thesupraoccipital slightly overlaps the interpar-ietal. This suture is better seen from thedorsal side of the isolated occipital complex.It has a very irregular dorsal edge, and anirregular area of overlap of up to ca. 2 mmacross the entire dorsal margin of thesupraoccipital.

FORAMINA CONTENTSAND HOMOLOGY

ACCESSORY PALATINE FORAMINA: Inthe dog (Evans, 1993), the accessory palatinenerve (nervus palatinus accessorius) arisesfrom the major palatine nerve (off thepterygopalatine nerve of V2) and suppliesthe caudal part of the hard palate. In thePteropus fetus, the accessory palatine nerves(those supplying the palate between themajor and minor palatine nerves) and ac-companying arteries reach the palate viasmall apertures in the lateral aspect of thehorizontal process of the palatine. On theright side there are three such foramina, andon the left there are five. Only the anterior-most one on the left arises directly from thepalatine canal (see below); the remainderoriginate posterior to the fully bone-enclosedportion of the palatine canal. P. lylei CM87972 has five small accessory palatineforamina per side in the lateral aspect of thepalatine, medial to the molars, situatedbetween the major and minor palatineforamina; the anterior three foramina aredependents of the palatine canal (fig. 9).

ALAR CANAL: See foramen ovale andsphenorbital fissure.

ALVEOLAR CANALS: In the dog (Evans,1993), alveolar canals carry branches of theinfraorbital nerve (of V2), artery, and vein tothe individual roots of the upper teeth andopen by numerous alveolar foramina at theapex of each alveolus (apex radici dentis).Within the maxilla posterior to the maxillaryforamen is an alveolar canal that transmitsthe caudal superior alveolar nerves to thecaudal cheek teeth. Within the infraorbital

canal are alveolar canals that transmit mid-dle and rostral superior alveolar nerves; thelatter enter the alveolar (5 incisivomaxillary)canals to be distributed to the upper canineand incisors. In the Pteropus fetus, the middleand rostral superior alveolar nerves andaccompanying blood vessels pass throughan alveolar canal in the maxilla (fig. 30)posterior to the maxillary foramen at thelevel of the last premolar and in the pre-maxilla (fig. 29). The top of the first molar isseparated from the pterygopalatine fossa bymembrane (the second molar has not yetformed), and the caudal superior alveolarnerves penetrate that membrane to reach thattooth. In P. lylei CM 87972, the alveolarcanal for the middle and rostral superioralveolar nerves is within the infraorbitalcanal on the left side and posterior to themaxillary foramen on the right (fig. 12). It islikely that the caudal superior alveolar nervesreach the first and second molars via theiropen roots, which are visible in the floor ofthe orbit.

BASICOCHLEAR FISSURE: The basico-chlear fissure (basicapsular fenestra) is a gapin the chondrocranium between the auditorycapsule laterally and the parachordal plate(central stem) medially (De Beer, 1937),bounded by anterior and posterior basico-chlear (basicapsular) commissures, if present(MacPhee, 1981). In some adult mammals,the fissure is not completely obliterated,resulting in the basicranial exposure of partof the inferior petrosal sinus (McDowell,1958). In the Pteropus fetus (figs. 34, 35), thebasicochlear fissure is bordered laterally bythe pars cochlearis of the petrosal, mediallyby the basioccipital, and posteriorly by thecartilaginous posterior basicochlear commis-sure. Anteriorly, the basicochlear fissure iscontinuous with the carotid foramen, becausethe anterior basicochlear commissure is lack-ing. The occupant of the basicochlear fissureis the inferior petrosal sinus, which connectsthe cavernous sinus to the internal jugularvein. The inferior petrosal sinus exhibitsconsiderable left-right asymmetry. Duringits course in the right basicochlear fissure,the inferior petrosal sinus principally sitswithin the cranial cavity but bulges into andout of the fissure and receives some smallveins from below. Its principal foramen of


exit is the jugular foramen, which it reachesby passing dorsal to the posterior basico-chlear commissure. On the left side, there isa significant drainage of the inferior petrosalsinus out of the posterior part of thebasicochlear fissure into the internal jugularsystem, in addition to that out the jugularforamen. In P. lylei CM 87972, the basico-chlear fissure is between the pars cochlearisof the petrosal laterally and the basioccipitalmedially and anteriorly (fig. 3). On thespecimen’s right side, the rostral entotympa-nic borders the basicochlear fissure antero-laterally, but on the left side this ossificationis missing and the basicochlear fissure iscontinuous with the carotid foramen. P. lyleiCM 87973 differs in that the basisphenoidcontributes to the anterior border of thebasicochlear fissure, and not the basioccipitalas in CM 87972.

In the dog (Evans, 1993), the ventralpetrosal sinus (5 inferior petrosal sinus) runsthrough the petro-occipital or petrobasilarcanal, between the petrous temporal andbasioccipital. The caudal opening of thepetro-occipital canal is anterior to the jugularforamen in the petro-occipital fissure (5basicochlear fissure of Pteropus).

CAROTID FORAMEN: In the dog (Evans,1993), the course of the internal carotidartery across the basicranium is withina perbullar canal (sensu Wible, 1986). Thereare three foramina associated with theartery’s course: one at its entrance into thecarotid canal, a second at its exit from thecanal, and a third at its entrance into thecranial cavity. As discussed by Wible andGaudin (2004), the associated nomenclatureemployed by Evans (1993) is confusing andcontradictory. Following Wible and Gaudin,we reserve the term carotid foramen for theforamen of entrance into the cranial cavity.In the Pteropus fetus (fig. 33), the carotidforamen lies between the anterior pole of thepars cochlearis of the petrosal posteriorly andthe cartilaginous central stem and sphenoidanteriorly (the basisphenoid and alisphenoidsare represented by one ossification center).The carotid foramen lacks medial and lateralborders (which would be the anterior basico-chlear and alicochlear commissures, respec-tively) and is continuous with the basico-chlear fissure medially and the piriform

fenestra laterally. Passing through the carotidforamen is the internal carotid artery andaccompanying nerve and vein. To reach thecarotid foramen, the artery, nerve, and veinfollow a short perbullar pathway, throughthe fibrous membrane of the tympanic cavity(sensu MacPhee, 1981; fig. 34), bordered bythe caudal entotympanic posterolaterally andthe rostral entotympanic anteromedially. InP. lylei CM 87972, the carotid foramen onthe right side is enclosed between the rostralentotympanic anteriorly and the anteriorpole of the promontorium posteriorly(fig. 10). The rostral entotympanic is missingon the specimen’s left side, and the carotidforamen’s anterior border is formed by thebasioccipital medially and the basi-/alisphe-noid laterally. Additionally, as in the fetus,the left carotid foramen is confluent with thebasicochlear fissure and the piriform fenestra.On both sides, a shallow carotid sulcus runssomewhat obliquely on the anterior pole ofthe promontorium to the carotid foramenfrom posteriorly and slightly medially. CM87973 differs in that the anterior border ofthe carotid foramen is formed by the basi-/alisphenoid laterally and the rostral entotym-panic medially.

CAUDAL PALATINE FORAMEN: See pal-atine canal.

CAVUM SUPRACOCHLEARE: See hiatusFallopii.

COCHLEAR CANALICULUS: In the dog(Evans, 1993), the perilymphatic duct entersthe petrous temporal (petrosal) via theexternal opening of the cochlear canaliculusin the rostral edge of the jugular foramen. Inthe Pteropus fetus, the perilymphatic ductenters the posteromedial aspect of the parscochlearis of the petrosal in the anterolateralaspect of the deep jugular foramen. Theexternal opening of the cochlear canaliculusis posteroventral to the posterior basico-chlear commissure, the bar of cartilageconnecting the cochlear capsule to the centralstem. Accompanying the perilymphatic ductinto the petrosal is a vein that drains into theinternal jugular. In P. lylei CM 87972, thecochlear canaliculus is not visible in directventral view, because it lies above the planeof the jugular foramen. As in the fetus, it liesin the anterolateral aspect of the jugularforamen. The placement of the cochlear


canaliculus in the isolated petrosal of P.livingstonii AMNH 274466 is shown infigure 14. Hinchcliffe and Pye (1969) de-scribed the cochlear aqueduct of Pteropusgiganteus as ‘‘duct type’’ with length greaterthan diameter, as compared to the ‘‘foramentype’’ of neglible length in the microchirop-terans they studied.

ETHMOIDAL FORAMEN: The dog (Evans,1993) has two ethmoidal foramina (some-times confluent): a smaller one in the suturebetween the frontal and orbitosphenoid and

a larger dorsocaudal one in the frontal. Theethmoidal nerve of V1 penetrates the rostralethmoidal foramen en route to the cribri-form plate and nasal cavity; the externalethmoidal artery, a branch of the externalophthalmic, occupies the caudal ethmoidalforamen. In the Pteropus fetus, the singleethmoidal foramen is between the frontal andala orbitalis (the chondrocranial precursor ofthe orbitosphenoid bone) and transmits theethmoidal nerve and external ethmoidalartery. In P. lylei CM 87972, the single,

Fig. 29. Pteropus sp. DUCEC 831, schematic representation of part of slide 7-1, a frontal sectionthrough the rostrum near the opening of the nasopalatine duct into the oral cavity at the front of theincisive fissure. The asterisk (*) represents a paired bar of cartilage connecting the lamina transversalisanterior in front to the palatine cartilage behind.


subcircular ethmoidal foramen lies in thefrontal, anterodorsal to the optic canal,about halfway between the orbital floor andthe postorbital process (fig. 11). P. lylei CM87973 differs in that the posterior border ofthe foramen is formed by the orbitosphenoid,and the foramen is considerably larger (largerthan the optic canal).

FORAMEN OVALE: In the dog (Evans,1993), the foramen ovale for the mandibularnerve (V3) and a small emissary vein is in thebase of the temporal wing of the basi-

sphenoid (alisphenoid); in the posterolateralborder of the foramen ovale, a small notch oreven a separate foramen spinosum for themiddle meningeal artery may be present.Anteromedial to the foramen ovale is thecaudal alar foramen, which transmits themaxillary artery (arteria maxillaris) and vein(vena maxillaris) into the alar canal (5alisphenoid canal of Gregory, 1910). In thePteropus fetus, the foramen for the mandib-ular nerve is within the basi-/alisphenoid,although the pterygoid approaches its ante-

Fig. 30. Pteropus sp. DUCEC 831, schematic representation of part of slide 10-1, a frontal sectionthrough the rostrum at the back of the incisive fissure. The paired palatine cartilage closes off the posteriorpart of the incisive fissure. On the left side, the deciduous lower canine (unlabeled) lies lateral to thepermanent canine.


romedial border and the squamosal ap-proaches its posterolateral border. Threemajor structures are transmitted (fig. 32):anteriorly the maxillary artery or ramusinfraorbitalis (sensu Wible, 1987), centrallyan emissary vein of the cavernous sinus, andposteriorly the mandibular nerve (V3). Con-sequently, the foramen ovale of Pteropusrepresents the foramen ovale + the caudalalar foramen of the dog (5 alisphenoidcanal). Positioned below the posterior edgeof the foramen ovale in the fetus is the oticganglion (ganglion oticum) off of V3 (fig. 33).A well-developed middle meningeal arterylike that in the dog is lacking; after themaxillary artery enters the foramen ovale itsends off two small meningeal branches tothe cavum epiptericum, an extradural spacehousing the trigeminal ganglion (gangliontrigeminale) and associated structures(Gaupp, 1902, 1905). In P. lylei CM 87972,the elongate foramen ovale is within thealisphenoid, although the pterygoid ap-proaches its medial border and the squamo-sal approaches its posterolateral border(figs. 3, 5, 10).

FORAMEN ROTUNDUM: See sphenorbi-tal fissure.

FORAMINA FOR FRONTAL DIPLOIC VEIN:Pteropus lylei CM 87972 has several smallforamina immediately ventral to the post-orbital process of the frontal (fig. 11). Basedon the fetus (fig. 31), the three foramina (twoon the right side) in the adult that are in closeassociation with the postorbital foramen (seebelow) transmit diploic veins; the moreposterior foramen transmits a small arteryand vein into the substance of the frontal.The artery is derived from the large orbitalartery, the external ophthalmic artery of theNAV (arteria ophthalmica externa), whichalso supplies the ethmoidal (arteria ethmoi-dalis), lacrimal (a. lacrimalis), and frontalarteries and the artery of the postorbitalforamen. The diploic veins represent thefrontal diploic veins (venae diploicae fron-tales), which have been described in varioustherians (see Thewissen, 1989; Evans, 1993;Wible, 2003; Wible and Gaudin, 2004).

FORAMINA FOR RAMI TEMPORALES: Fol-lowing Wible and Gaudin (2004), we use theterm foramina for rami temporales foropenings in the squamosal dorsal to the

suprameatal bridge transmitting rami tem-porales of the stapedial artery and accom-panying veins to the m. temporalis. Thisterm is equivalent to subsquamosal foram-ina of Wible et al. (2004). The dog has noforamina for rami temporales, and thevascular supply to the m. temporalis followsan entirely extracranial course via theexternal carotid system (Evans, 1993). Inthe Pteropus fetus, there are two foramina forrami temporales per side between the parietaland squamosal transmitting arteries andveins. The arteries are derived from theposterior division of the ramus superior(fig. 35), and the veins connect to thecapsuloparietal emissary vein anteriorly andthe vena diploetica magna posteriorly in theposttemporal canal. The more anterior fora-men for ramus temporalis lies above theentrance of the capsuloparietal emissary veininto the squamosal bone endocranially (seepostglenoid foramen), and the posterior onelies above the anterior end of the posttem-poral canal. In P. lylei CM 87972, thedorsally directed foramina for rami tempor-ales are between the parietal and the squa-mosal, dorsal to the external acoustic meatus,with short sulci carrying the contents ontothe parietal (fig. 2). There are two smallopenings on the left side and a single, largeropening on the right. CM 87973 has twoforamina on the right and three on the left.

GLASERIAN FISSURE: According to Klaauw(1931: 164), during ontogeny, the Glaserianfissure (fissura Glaseri) forms first in theanterior wall of the presumptive auditorybulla as an aperture for Meckel’s cartilage.Meckel’s cartilage subsequently disappearsand ‘‘later on we find the chorda tympaninerve in it and often the ramus inferior ofthe stapedial artery’’. As the elementsforming the auditory bulla vary amongmammals (Klaauw, 1931; Novacek, 1977),so do the elements forming the Glaserianfissure. In the dog (Evans, 1993), the chordatympani nerve (chorda tympani) passesthrough a small canal in the anterodorsalwall of the auditory bulla and emergesthrough the petrotympanic fissure by asmall opening medial to the postglenoidprocess. In the Pteropus fetus, Meckel’scartilage and the chorda tympani nerve leavethe middle ear via a wide gap floored by the


gonial, roofed by the squamosal, and withopen medial and lateral walls (fig. 33).According to Fleischer (1973), the gonial(rostral process of the malleus in part) isfused to the anterior crus of the ectotympa-nic in adult Pteropus, but in P. lylei CM87971–87973, seams still distinguish theseelements. In P. lylei CM 87971 and 87973,the Glaserian fissure is actually a foramenbetween the gonial and squamosal, witha distinct groove for the nerve present onthe dorsal surface of the gonial.

HIATUS FALLOPII: In the dog (Evans,1993), the greater petrosal nerve runs for-ward from the geniculate ganglion (gangliongeniculi) of the facial nerve within the petroustemporal (petrosal) in a canal termed thepetrosal canal, dorsal to the fossa for the m.tensor tympani. It exits the petrosal canal ata small aperture near the distal end of thepetrosquamous suture. For the openingtransmitting the greater petrosal nerve fromthe petrosal, we employ the term hiatusFallopii (McDowell, 1958); for the space

Fig. 31. Pteropus sp. DUCEC 831, schematic representation of part of slide 42-1, a frontal sectionthrough the orbit at the postorbital process. The artery of the postorbital foramen penetrates thepostorbital foramen in the postorbital process, and the frontal nerve, artery, and vein pass anteroventral tothe postorbital process. On the left side, a frontal diploic vein (unlabeled) enters a small foramen medial tothe postorbital foramen. For cartilage ‘‘N’’, we follow Jurgens (1963: 19), who named it in Rousettusaegyptiacus as an enigmatic ‘‘discrete convex cartilaginous plate in the orbit . . . it lies medio-dorsally to theanterior part of the sclera with its dorsal edge in the upper eyelid and its ventral part embedded in glands.’’In Pteropus sp., it is closely associated with the m. levator palpebrae superioris.


housing the geniculate ganglion, we employthe term cavum supracochleare (Voit, 1909).In the Pteropus fetus, a bone-enclosed hiatusFallopii is lacking, as is a bone-enclosedcavum supracochleare. The geniculate gan-glion sits in a depression on the top of thepars cochlearis, and the greater petrosalnerve runs forward also on top of the parscochlearis, accompanied by a vein that drainsinto the cavernous sinus (fig. 35). In P. lyleiCM 87972, the hiatus Fallopii is hidden fromview. However, in P. livingstonii AMNH274477, which has isolated petrosals, thehiatus Fallopii is represented by a well-de-veloped, balloon-shaped opening best viewedin lateral view (fig. 15). Forming the roof ofthis aperture is the ossified prefacial commis-sure (suprafacial commissure of Jurgens,1963). The hiatus Fallopii appears to belarger than the structures that it transmits;one can see into the cavum supracochleareand view both the primary and secondaryfacial foramina from the hiatus. Reconstruct-ing the isolated petrosal onto the skull, it isapparent that the hiatus Fallopii opens abovethe plane of the piriform fenestra. Therefore,the greater petrosal nerve exits the piriformfenestra to join the internal carotid (deeppetrosal) nerve (nervus caroticus interna)beneath the carotid foramen.

HYPOGLOSSAL FORAMEN: In the dog(Evans, 1993), the hypoglossal foramen, theexternal opening of the hypoglossal canal(canalis nervum hypoglossum), is in theexoccipital bone, posterolateral to the jugularforamen; it transmits the hypoglossal nerveand vein. In the Pteropus fetus, the hypo-glossal foramen is nearly entirely within theexoccipital ossification; the anteromedialborder is formed by the cartilage in thechondrocranium’s central stem that separatesthe exoccipital and basioccipital ossifications.Transmitted are the hypoglossal nerve (ner-vus hypoglossus) and vein (vena canalishypoglossi) and a caudal meningeal branch(arteria meningea caudalis) of the occipitalartery (arteria occipitalis). Sutures delimitingthe exoccipital and basioccipital are not fullypreserved in P. lylei CM 87972 (see fig. 5).However, the sutures are preserved in Pter-opus temminckii AMNH 194276, and thehypoglossal foramen is entirely within theexoccipital.

INCISIVE FISSURE: The dog (Evans,1993) has paired palatine fissures (5 incisiveforamina of this report) largely in the incisivebone (5 premaxilla of this report) but withthe posterior border formed by the maxilla.The occupants are the nasopalatine duct(ductus incisivus) connecting the vomeronasalorgan (organum vomeronasale) to the oraland nasal cavities (cavum oris and cavum nasi,respectively), the rostral septal branches(rami septi rostrales) of the major palatineartery of V2 (arteria palatina major), and theseptal branch of the caudal nasal nerve of V1

(nervus nasopalatinus). In contrast, Pteropuslylei has one large gap between the premax-illae and maxillae in the anterior hard palate,which we call here the incisive fissure (figs. 3,9). In the Pteropus fetus, the incisive fissure isnot as large as it appears in macerated adultskulls, because it is floored posteriorly bypaired palatine cartilages that abut eachother on the midline, dorsomedially by theanterior paraseptal cartilages, and laterallyby the premaxillae (figs. 29, 30). Thesecartilages correspond to, but are much largerthan, the cartilago palatini described byJurgens (1963); each palatine cartilage iscontinuous anteriorly with the lamina trans-versalis anterior (fig. 29). The major occu-pants of the gap anterior to these cartilagesare the paired nasopalatine ducts (fig. 29),which connect the oral and nasal cavities; thevomeronasal organ is lacking. In addition,there are several paired nasal cartilages thatextend into the incisive fissure from above:the nasopalatine duct cartilage, which coversthe anterior surface of the nasopalatine duct,and the ventral part of the lamina transver-salis anterior, which is interposed betweenthe nasopalatine duct cartilage and theparaseptal cartilage. Also anteromedial tothe exits of the nasopalatine ducts are theseptal branches of the paired caudal nasalnerves of V2, also called the nasopalatinenerves (fig. 29). No major vessels are trans-mitted. However, there is a tiny midline gapbetween the maxillae and palatine cartilagesthat transmits an artery from the palate intothe nasal cavity. This artery runs forwardunder the nasal septum and divides into rightand left arteries to the tip of the snout.

INFRAORBITAL CANAL, INFRAORBITAL

FORAMEN, AND MAXILLARY FORAMEN: In


the dog (Evans, 1993), the infraorbital canalcarries the infraorbital nerve of V2 (nervusinfraorbitalis), artery (arteria infraorbitalis),and vein (vena infraorbitalis) from the orbitto the snout. The anterior opening of eachinfraorbital canal on the snout, the infra-orbital foramen, is within the maxilla, andthe posterior opening in the orbit, themaxillary foramen, is between the maxilla,lacrimal, and jugal. The infraorbital canal isroughly the same length as the enlargedupper carnassial tooth (dens sectorius), theultimate upper premolar. In Pteropus lyleiCM 87972, the infraorbital canal is entirely

within the maxilla, dorsal to the M1 (figs. 2,12). Its anterior opening on the face, theinfraorbital foramen, and its posterior open-ing in the orbit, the maxillary foramen, arenearly contiguous because the infraorbitalcanal is very short. The orbital process of thelacrimal approaches but does not quitecontribute to the dorsal margin of themaxillary foramen. Based on the Pteropusfetus, the infraorbital canal transmits theinfraorbital nerve, artery, and vein (visiblewithin the orbit in fig. 31).

INTERNAL ACOUSTIC MEATUS: For theinternal acoustic meatus, we rely on the

Fig. 32. Pteropus sp. DUCEC 831, schematic representation of part of slide 63-1, a frontal sectionthrough the temporal fossa at the foramen ovale and fossa hypophysialis. The basisphenoid (housing thefossa hypophysialis) and alisphenoids (housing the foramen ovale) are a single ossification. In sectionsrostral to this one, the nerve of the pterygoid canal enters the pterygoid canal between the pterygoid andsphenoid. The inferior alveolar nerves and vessels (unlabeled) lie between the mandible andMeckel’s cartilage.


anatomy of the horse (Sisson, 1910), forwhich greater detail is provided than for thedog. In the horse, the internal acousticmeatus is a short canal on the endocranialsurface of the petrous temporal (petrosal)that transmits the facial and vestibuloco-chlear nerves (nervus facialis and nervusvestibulocochlearis, respectively) and the in-ternal auditory artery (arteria labyrinthi) offthe basilar artery (arteria basilaris). It isdivided by a transverse crest into dorsal andventral depressions, the foramen acusticumsuperius and inferius, respectively. In theanterior part of the foramen acusticumsuperius is the area nervus facialis, the cranialopening of the facial canal, and in theposterior part is the dorsal vestibular areaperforated by foramina transmitting nervesto the utricle and the ampullae of the anteriorand lateral semicircular canals. In the fora-men acusticum inferius is the area cochleae,a central foramen with a spiral tract ofminute foramina (tractus spiralis foramino-sus) for fascicles of the cochlear nerve (nervuscochlearis). Posterior to this are small open-ings transmitting nerves to the saccule anda foramen singulare for the nerve to theampullae of the posterior semicircular canal.As described by Evans (1993), the internalacoustic meatus of the dog conforms to thispattern, although the details of nervouspassages are not as thoroughly described.Rather than a canal, however, the internalacoustic meatus of the dog is an irregularlyelliptical depression, and the opening into thedepression is the external acoustic porus(porus acusticus externus). The internalacoustic meatus in the isolated petrosals ofPteropus livingstonii AMNH 274477 con-forms to the pattern of that in the dog(fig. 14). The meatus is figure eight–shaped,with the dorsal depression smaller than theventral one. Visible within the dorsal de-pression is the aperture by which the facialnerve reaches the cavum supracochleare andthe small dorsal vestibular area. Visiblewithin the anterior part of the ventraldepression are two central foramina perfo-rated by tiny apertures for the cochlearnerves. Posterior to this are small openings,but we were unable to distinguish one as theforamen singulare. In the Pteropus fetus, theinternal acoustic meatus resembles that in the

dog and adult with one principal exception:the nerves to the saccule and ampulla of theposterior semicircular canal pass througha single opening. A separate foramen singu-lare is reported for fetal Rousettus aegyptia-cus (Jurgens, 1963) but not for fetal R.leschenaulti (5 Pteropus seminudus; Starck,1943).

JUGULAR FORAMEN: In the dog (Evans,1993), the jugular foramen is between thepetrous temporal (petrosal) and the occipital;based on the disarticulated skull of a puppy(Evans, 1993: fig. 4–45), it appears to belargely or wholly the exoccipital bone thatborders the jugular foramen. After exitingthrough the jugular foramen, its contents—the glossopharyngeal (cranial nerve IX),vagus (X), and accessory nerves (XI; i.e.,nervus glossopharyngeus, nervus vagus, andnervus accessorius, respectively) and thesigmoid sinus (sinus sigmoideus)—then passthrough the petro-occipital and tympano-occipital fissures to reach the skull base. Inthe Pteropus fetus, the borders of the jugularforamen are formed by the petrosal laterallyand the exoccipital medially, with the un-ossified portions of the chondrocranium thatconnect these bones forming the anterior andposterior borders. Occupying the jugularforamen from front to back are the internaljugular vein, the glossopharyngeal, vagus,and accessory nerves, and a caudal meningealbranch of the occipital artery. In the dog, thesigmoid sinus and inferior petrosal sinus jointo form the internal jugular vein below theskull base. In the Pteropus fetus, the principalexit of the sigmoid sinus is the foramenmagnum, but it does have a connection withthe inferior petrosal sinus intracranially, withthe internal jugular vein then exiting thejugular foramen. P. lylei CM 87972 preservesthe part of the suture between the basiocci-pital and exoccipital near the jugular foramen(figs. 3, 5). It shows that foramen is borderedby the pars cochlearis of the petrosalanteriorly, the pars canalicularis of thepetrosal laterally, and the exoccipital medi-ally and posteriorly on the left side. On theright side, the basioccipital has a very narrowmedial contribution.

LACRIMAL FENESTRA: The right side ofPteropus lylei CM 87973 has a small, ovalopening in the suture between the orbital


processes of the lacrimal and frontal, slightlybelow the level of the lacrimal foramen; thespecimen’s left side has a shallow pit there, asis present bilaterally in CM 87972 (fig. 12).Based on the Pteropus fetus, this accommo-dates one of the extraocular muscles, theinferior oblique (musculus obliquus ventralis),which attaches to the lacrimal and theunderlying nasal capsule. A similar arrange-ment has been reported for the yellowarmadillo, with the aperture called thelacrimal fenestra (Wible and Gaudin, 2004).

LACRIMAL FORAMEN: In the dog (Evans,1993), there is a large opening in the centerof the orbital process of the lacrimal calledthe fossa for the lacrimal sac (fossa saccilacrimalis). The lacrimal sac is formed by theunion of the two lacrimal ducts (each onea canaliculus lacrimalis), one from each eyelid(palpebra), and in turn leads into the lacrimal

canal, which transmits the nasolacrimal ductforward to the nasal vestibule (vestibulumnasi). Here, we use the term foramenlacrimale from the NAV for the bonyaperture that transmits the nasolacrimal ductfrom the lacrimal fossa to the lacrimal canal.In Pteropus lylei CM 87972, the largelacrimal foramen is in the anteroventralaspect of the facial process of the lacrimal,with the maxilla forming its ventral margin(figs. 2, 12). Based on the Pteropus fetus, thesole occupant of the lacrimal foramen is thenasolacrimal duct.

MAJOR PALATINE FORAMEN: In the dog(Evans, 1993), the major palatine nerve(nervus palatinus major) off the pterygopala-tine nerve of V2 (nervus pterygopalatinus)supplies the rostral hard palate, which itreaches via the major palatine foramen at thepalatomaxillary suture. In the Pteropus fetus,

Fig. 33. Pteropus sp. DUCEC 831, schematic representation of part of slide 68-2, a frontal sectionthrough the basicranium at the carotid foramen, which is continuous laterally with the front of thepiriform fenestra and posteriorly with the basicochlear fissure. The chorda tympani nerve (unlabeled) liesin the Glaserian fissure, between the ramus inferior and otic ganglion medially, and Meckel’s cartilage, thegonial, and the anterior crus of the ectotympanic laterally.


the major palatine nerve and artery (arteriapalatina major) arise from the pterygopala-tine nerve of V2 within the orbit (fig. 31), runthrough the caudal palatine foramen into thepalatine canal (see below), and exit onto thehard palate along the anterior contactbetween the palatine and maxilla. The rightside of the fetus has two major palatineforamina: a larger anterior one in the trans-verse palatine suture, as on the left side, anda smaller posterior one wholly within thepalatine. In P. lylei CM 87972, the majorpalatine foramen lies in or in front of theanteriormost suture between the palatine andmaxilla and has a short palatine sulcusextending forward from it on the maxilla(figs. 3, 9).

MANDIBULAR FORAMEN: In the dog(Evans, 1993), the mandibular foramen isthe caudal opening of the mandibular canalfor the inferior alveolar nerve (nervus alveo-laris inferior) and vessels (arteria alveolarisinferior et vena alveolaris inferior); it is locatedon the medial side of the mandibular ramus,roughly in the anterior–posterior center,below the alveolar plane of the mandibulardentition. In Pteropus lylei CM 87972, theposteriorly directed mandibular foramen iscentrally located on the mandibular ramus.Extending posteriorly and slightly dorsallyfrom the foramen is a deep sulcus, the dorsalborder of which is formed by a low crest thatnearly reaches to the condyle. In the fetus,the inferior alveolar nerve, artery, and vein

Fig. 34. Pteropus sp. DUCEC 831, schematic representation of part of slide 71-2, a frontal sectionthrough the basicranium at the postglenoid process. The gap between the petrosal and alisphenoid is theback of the piriform fenestra; the gap between the petrosal and basisphenoid is the front of thebasicochlear fissure. The internal carotid artery runs through a mass of connective tissue fibers, the fibrousmembrane of the tympanic cavity of MacPhee (1981). The chorda tympani nerve (unlabeled) penetratesa foramen in the gonial. The anterior division of the ramus superior penetrates a foramen in the ventralaspect of the parietal, which represents the epitympanic wing. The capsuloparietal emissary vein liesbeneath the postglenoid process; the postglenoid foramen is in sections rostral to this one.


first run in a deep sulcus on the mandibularramus that is then covered laterally byMeckel’s cartilage (fig. 32) and then ultimate-ly enclosed in the mandible.

MASTOID FORAMEN: In the dog (Evans,1993), the mastoid foramen is on the occiputbetween the exoccipital, supraoccipital, andmastoid process (5 mastoid exposure of thepetrosal of this report); it transmits theoccipital emissary vein (vena emissaria occi-pitalis), which drains the deep muscles on thecranial part of the neck into the sigmoidsinus. Evans (1993: 608) also reporteda caudal meningeal artery off the occipitalartery that ‘‘goes through the supramastoidforamen and ramifies in the dura of theoccipital cranial fossa’’. The supramastoidforamen is not mentioned elsewhere in thetext, and we speculate that it may in fact be

the mastoid foramen. In the Pteropus fetus,the mastoid foramen is at the junction of thepars canalicularis of the auditory capsule(capsula otica), exoccipital, and supraoccipi-tal and transmits the occipital emissary veinto the sigmoid sinus. In P. lylei CM 87972,the small mastoid foramen (0.4 mm on theleft and smaller on the right) is between themastoid exposure of the petrosal and theoccipital (the ex- and supraoccipital beingfused; fig. 5); the left mastoid foramen in CM87973 is comparable in size, but the right oneis twice as large. In Pterotus capistratusAMNH 194276, a very small mastoid fora-men is present on the left side only at thejunction of the exoccipital, supraoccipital,and petrosal.

MAXILLARY FORAMEN: See infraorbitalcanal.

Fig. 35. Pteropus sp. DUCEC 831, schematic representation of part of slide 75-1, a frontal sectionthrough the basicranium at the epitympanic recess over the mallear-incudal articulation. The inferiorpetrosal sinus lies in the basicochlear fissure between the petrosal and basioccipital. The posterior divisionof the ramus superior occupies a sulcus in the ventral aspect of the parietal, which represents theepitympanic wing. The part of the tegmen tympani here is the near vertical component; ventral to it is thetensor tympani muscle’s attachment to the malleus, and medial to it is the distal remnant of the stapedialartery, which fails to reach the stapes.


MENTAL FORAMINA: The dog has sev-eral mental foramina per side that transmitthe mental nerves (nervi mentales), artery(arteria mentalis), and vein (vena mentalis)from the mandibular canal (Evans, 1993).The largest, the middle mental foramen, isbeneath the embrasure between the first twocheek teeth. An anterior one is positionedbeneath the central incisor, and one or moresmall foramina are positioned caudal to themiddle mental foramen. Pteropus lylei CM87972 has two mental foramina per side:a larger posterior mental foramen beneath p1and an anterior mental foramen beneath theembrasure between the first and secondincisors (fig. 6). The fetus also has twomental foramina, both of which transmitmental nerve, artery, and vein: a medial onejust off the midsagittal line beneath the i1 anda lateral one beneath the first deciduouspremolar.

MINOR PALATINE FORAMINA: In thedog (Evans, 1993), the minor palatine nerve(nervus palatinus minor) off the pterygopala-tine nerve of V2 supplies the soft palate, andthe caudal part of the hard palate is suppliedby an accessory palatine nerve off the majorpalatine nerve, which in turn supplies therostral hard palate. In the Pteropus fetus, thenerves that supply the soft palate also supplythe caudal hard palate. We identify these asminor palatine nerves and their foramina inthe palate as the minor palatine foramina,following Wible and Rougier (2000). As inthe dog, the minor palatine nerves in thePteropus fetus arise from the pterygopalatinenerve off V2 lateral to the m. pterygoideusmedialis and pass through three asymmetri-cally arranged, small foramina in the pos-terolateral border of the palatine, accompa-nied by branches of the minor palatine artery(arteria palatina minor) derived from themaxillary artery (arteria maxillaris). In P.lylei CM 87972, the two posteriormostforamina on the left palatine are directedmedially and caudally, respectively, andidentified by us as minor palatine foramina;on the right side there are three, two directedmedially and one caudally (fig. 9).

OPTIC CANAL: In the dog (Evans, 1993),the optic canal (canalis opticus) is in thecenter of the orbital wing of the presphenoidbone (orbitosphenoid) and transmits the

optic nerve (nervus opticus), the internalophthalmic artery (arteria ophthalmica in-terna, 5 ophthalmic artery of this report) offthe Circle of Willis (circulus arteriosus cere-bri), and the internal ophthalmic vein (venaophthalmica interna). In the Pteropus fetus,the optic canal is between the presphenoidand orbitosphenoid ossification centers with-in the orbital cartilages and transmits thesame structures as in the dog. Also as in thedog, within the orbit the ophthalmic arteryjoins the external ophthalmic artery (5 theramus orbitalis of Wible, 1987). In P. lyleiCM 87972, the presphenoid and orbitosphe-noid are fused seamlessly. As interpreted byus, the floor of the ovoid optic canal isformed by the presphenoid and the remainingborders by the orbitosphenoid (fig. 11).

ORBITOTEMPORAL CANAL: In variousextant placentals, the anterior division ofthe ramus superior of the stapedial artery(and accompanying vein) extends from itsendocranial origin above the front of themiddle ear to the orbit in a channel called thesinus canal (Gregory, 1910; McDowell, 1958)or the orbitotemporal canal (Rougier et al.,1992; Wible et al., 2004). We prefer the latterterm, because it best describes the position ofthis vascular canal, and it best reflects thebroader homology of these structures, havingalready been applied to a broad spectrum ofcynodonts (see Rougier et al., 1992). Theorbitotemporal canal and its orbital openingare lacking in the dog (Evans, 1993). In thePteropus fetus, the anterior division of theramus superior arises over the anterolateralaspect of the middle ear in the extracranialspace roofed by the epitympanic wing of theparietal and floored by the squamosal andthe tympanic roof. The artery enters thecranial cavity via a foramen in the ventrolat-eral aspect of the parietal epitympanic wing(fig. 34) and runs anterodorsolaterally alongthe medial surface of the parietal (fig. 33). Itenters a gap between that bone laterally andthe back of the ala orbitalis (the cartilaginousprecursor of the orbitosphenoid) mediallyand disappears. The existence of the orbito-temporal canal, such as in the fetus, cannotbe studied in the intact Pteropus skulls.However, in P. livingstonii AMNH 274517,a disarticulated skull, the endocranial sur-faces of the squamosals and parietals can be


studied. Ventral to the endocranial apertureby which the capsuloparietal emissary veinenters the squamosal, there is a deep, nearlyvertical sulcus for the posterior division ofthe ramus superior. In the anteroventralmargin of this sulcus is a notch that leadsinto a shallow, longitudinal sulcus for theanterior division of the ramus superior thatruns forward on the endocranial surface ofthe parietal to the level of the anterior extentof the squamosal. This shallow sulcus repre-sents the open channel for the orbitotemporalcanal.

PALATINE CANAL: In the dog (Evans,1993), the course of the major palatine nerveand artery from the pterygopalatine fossa tothe palate is via a palatine canal in thehorizontal process of the palatine. Theposterior opening into the palatine canal isthe caudal palatine foramen (Schaller, 1992).In the Pteropus fetus, the palatine canal isonly fully enclosed within the palatine in thecentral portion of the nerve’s course throughthat bone. Posteriorly, between the minorpalatine foramina and the caudal palatineforamen, the major palatine nerve and arteryoccupy a deep sulcus that is open dorsallyinto the pterygopalatine fossa (fig. 31). It is inthe ventral floor of this sulcus that all but oneof the accessory palatine foramina are found.Anteriorly, just behind the major palatineforamen, there is another sulcus for the majorpalatine nerve and artery that is opendorsally in the floor of the nasopharyngealmeatus. In P. lylei CM 87972, a posteriorsulcus is clearly retained in the pterygopala-tine fossa and leads to the posterior openinginto the palatine canal, opposite the anteriorroot of the last molar, M2 (fig. 12). Theexistence of an anterior sulcus as in the fetuscannot be confirmed or denied in the adultwithout CT scans of the specimen.

PIRIFORM FENESTRA: The piriform fe-nestra is the large gap present in all fetalmammals and in a few adults anterior to theauditory capsule, usually between that ele-ment, the sphenoid (basi- and alisphenoid),and the squamosal (MacPhee, 1981). Theseelements are in close contact in the adult dog(Evans, 1993), and, therefore, the piriformfenestra is absent. In the Pteropus fetus, thepiriform fenestra is between the anterior poleof the promontorium and the basi-/alisphe-

noid and is continuous medially with thecarotid foramen (there being no alicochlearcommissure). Flooring the piriform fenestrais the rostral entotympanic. Running acrossthe piriform fenestra dorsal to this cartilage isthe greater petrosal nerve, which joins theinternal carotid (deep petrosal) nerve beneaththe carotid foramen. Entering the cavumepiptericum via the piriform fenestra area nerve connecting the greater petrosal nerveand the mandibular nerve and a vein drainingfrom the auditory capsule to the cavernoussinus. In P. lylei CM 87972, the piriformfenestra is an obliquely oriented, roughlycigar-shaped opening between the anteriorpole of the promontorium and the alisphe-noid (figs. 3, 5, 10); the epitympanic wing ofthe parietal approximates but does notcontribute to the posterolateral border. Thepiriform fenestra is continuous medially withthe carotid foramen; these apertures areseparated by a narrow petrosal-alisphenoidcontact in CM 87973.

POSTGLENOID FORAMEN: In the dog(Evans, 1993), the retroarticular foramen (5postglenoid foramen) lies in the squamouspart of the temporal bone (5 squamosal),behind the retroarticular process (5 post-glenoid process). It transmits the retroarticu-lar vein (5 postglenoid vein or capsulopar-ietal emissary vein of Gelderen, 1924),a major distributary of the transverse sinus(sinus transversus). In the Pteropus fetus, overthe back of the auditory capsule the trans-verse sinus divides into a posteroventrallydirected sigmoid sinus and an anteriorlydirected sinus. The latter soon divides intothe dorsal petrosal sinus and the capsulopar-ietal emissary vein. The capsuloparietalemissary vein continues forward into a spaceat first between the dorsolateral aspect of thepars canalicularis of the auditory capsule andthe parietal, but then bordered by thesquamosal bone as well; passing throughthe anterior part of this space is the ramussuperior of the stapedial artery. Over theepitympanic recess, the capsuloparietal emis-sary vein enters the squamosal bone (fig. 35).Anterolateral to the epitympanic recess (re-cessus epitympanicus), the vein leaves thesquamosal via the postglenoid foramen incompany with a tiny artery off the posteriorauricular artery (arteria auricularis caudalis).


In P. lylei CM 87972, the postglenoidforamen is in the squamosal, although theanterior crus of the ectotympanic approachesits posteromedial margin (figs. 3, 5, 11). Onthe right side of P. lylei CM 87973, thealisphenoid approaches the anteromedialmargin as well.

POSTORBITAL FORAMEN: The name post-orbital (or frontal) foramen for the largeopening in the anterior root of the post-orbital process of the frontal bone has beenregularly used in the megachiropteran liter-ature since the nineteenth century (seereferences in Andersen, 1912). Prior to ourstudy, we anticipated that the occupants ofthe postorbital foramen in Pteropus were thefrontal nerve of V1 (nervus frontalis) andaccompanying vessels, which occupy analo-gous positions in other placentals (e.g., therabbit, Bensley, 1931; the dog, Evans, 1993).If true, the postorbital foramen of Pteropuswould be analogous to the supraorbitalforamen of human anatomy, as Andersen(1912) proposed. However, in the fetus(fig. 31), the frontal nerve and accompanyingvessels leave the orbit anterior to the post-orbital process and move laterally onto theside of the snout. Instead, the postorbitalforamen transmits a tiny branch of thefrontal nerve and a large artery and vein.The large artery runs anteriorly along thefrontal bone and then along the nasomax-illary suture to ramify in the tip of the snout(figs. 29, 30). Within the orbit, the largeartery and vein ultimately join the vesselsaccompanying the frontal nerve (fig. 31). Weare uncertain what to name this large artery,because that accompanying the frontal nerveis best called the postorbital (supraorbital)artery. Because this vessel with its longrostral course is to our knowledge unique,we have chosen to call it the artery of thepostorbital foramen.

POSTTEMPORAL CANAL: In monotremesand some placentals, the posterior division ofthe ramus superior of the stapedial artery, thearteria diploetica magna of Hyrtl (1853,1854), and an accompanying vein travel ina canal between the petrosal and squamosalthat opens onto the occiput (Wible, 1987;Wible and Hopson, 1995). For this channel,we employ the term posttemporal canal,which is widely used in the literature of

nonmammalian cynodonts (Wible, 1989;Rougier et al., 1992). The posttemporal canalis wholly absent in the dog. The Pteropusfetus has a short segment of the posttemporalcanal, but it is a blind canal with no egress onthe occiput. It begins anteriorly beneath theposterior foramen for ramus temporaliswhere the tiny continuation of the posteriordivision of the ramus superior or arteriadiploetica magna and a sizable vein entera canal between the squamosal, parietal, andpars canalicularis of the auditory capsule,just above the fossa incudis. Behind theposterior extent of the squamosal, the canalcontinues posteriorly a short distance be-tween the parietal and the gyrus of theanterior (superior) semicircular canal. Theartery disappears, whereas the vein runsendocranially over the pars canalicularis intothe transverse sinus. Regarding the existenceof the posttemporal canal in adult Pteropus,we were not able to identify any groovesindicating this canal on the isolated petrosals,squamosals, and parietals studied with P.livingstonii AMNH 274477 and 274517.

PTERYGOID CANAL: In the dog (Evans,1993), an extremely small pterygoid grooveon the basisphenoid runs anteriorly intoa minute pterygoid canal. The caudal open-ing of the pterygoid canal is in the suturebetween the basisphenoid and pterygoid, andthe rostral opening is in the caudal part of thepterygopalatine fossa, between the pterygoidand pterygoid process of the sphenoid (theventral projection of the sphenoid that abutsthe pterygoid bone). Transmitted are thenerves of the pterygoid canal (nervus canalispterygoidei) and occasionally a small arteryof the pterygoid canal off the maxillaryartery. In the Pteropus fetus, the greaterpetrosal nerve (nervus petrosus major) andinternal carotid (deep petrosal) nerve formthe nerve of the pterygoid canal beneath thecarotid foramen. The nerve of the pterygoidcanal runs forward between the basi-/ali-sphenoid and the tiny tubal cartilage, andthen enters the cavum epiptericum viaa foramen between the basi-/alisphenoidand the underlying pterygoid (fig. 32). Withinthe cavum epiptericum, the nerve enters thepterygopalatine ganglion off V2. During itscourse within the cavum, the nerve isaccompanied by a tiny artery off the maxil-


lary artery. In P. lylei CM 87973, the nerve ofthe pterygoid canal runs in a tiny, obliquecanal between the basisphenoid and rostralentotympanic immediately anterior to thecarotid foramen. It then crosses the ventro-lateral surface of the basisphenoid withoutany bony impression and enters a smallforamen in the suture between the basi-sphenoid and pterygoid. The foramen openswithin the braincase, but it can be viewed viathe sphenorbital fissure. The placement of thecaudal opening of the pterygoid canal in P.lylei CM 87972 is indicated in figure 10.

SECONDARY FACIAL FORAMEN: In thedog (Evans, 1993), the course of the facialnerve through the petrous temporal (petro-sal) between the internal acoustic meatusendocranially and the stylomastoid foramenon the skull base is entirely within a bonyfacial canal. In Pteropus livingstonii AMNH274477, the course of the facial nerve throughthe middle ear is within a sulcus that is walledlaterally by the crista parotica (De Beer,1937) and ends posteriorly at the stylomas-toid notch. To reach this sulcus, the facialnerve passes from the internal acousticmeatus endocranially to the cavum supraco-chleare within the petrosal to the middle ear,the cavum supracochleare (Voit, 1909) beingthe space housing the geniculate ganglion.Following Wible (1990), we identify theforamen of entrance into the cavum supraco-chleare from the internal acoustic meatus asthe primary facial foramen, and the foramenof entrance into the middle ear from thecavum supracochleare as the secondary facialforamen. The secondary facial foramen in P.livingstonii AMNH 274477 is fully enclosedin bone and lies anterolateral to the fenestravestibuli (fig. 13). In the Pteropus fetus, thesecondary facial foramen is not yet fullyenclosed in bone and/or cartilage and isrepresented by a notch in the anterolateralaspect of the pars cochlearis of the petrosal.

SPHENOPALATINE FORAMEN: In the dog(Evans, 1993), the caudal nasal nerve (nervusnasalis caudalis) off the pterygopalatine nerveof V2 and sphenopalatine artery (arteriasphenopalatina) and vein (vena sphenopala-tina) leave the pterygopalatine fossa andenter the nasal cavity via the sphenopalatineforamen (foramen sphenopalatinum) in thepalatine bone, which lies just dorsal to the

caudal palatine foramen. The Pteropus fetushas two foramina in the palatine dorsolateralto the palatine canal that transmit caudalnasal nerves and sphenopalatine arteries intothe nasopharyngeal meatus and nasal cavity.The larger, anteroventral foramen sendsnerves and vessels forward into the ventro-lateral aspect of the nasal cavity, and thesmaller, posterodorsal foramen sends nervesand vessels forward along the ventromedialaspect of the nasal cavity, lateral to thevomer. The latter nerves and vessels reachtheir foramen in the palatine via a coursethrough the origin of the m. pterygoideusmedialis, whereas the former run ventral tothat muscle. P. lylei CM 87973 has twoopenings in the palatine that probablycorrespond to the two sphenopalatine foram-ina occurring in the fetus, whereas CM 87972has only one (fig. 12). These foramina lieanterior and dorsal to the caudal palatineforamen.

SPHENORBITAL FISSURE: In the dog(Evans, 1993), the orbital fissure (fissuraorbitalis) lies lateral to the body of thesphenoid in the suture between the orbitaland temporal wings (orbito- and alisphe-noid). It transmits the oculomotor (cranialnerve III), trochlear (IV), ophthalmic (V1),and abducens nerves (VI; i.e., nervus oculo-motorius, nervus trochlearis, nervus ophthal-mica, and nervus abducens, respectively), theanastomotic artery (arteria anastomotica)connecting the maxillary and internal carotidarteries, and the ophthalmic venous plexus(plexus ophthalmicus). The maxillary nerve(cranial nerve V2, nervus maxillaris) hasa foramen of exit separate from the ophthal-mic nerve: the foramen rotundum into thesubstance of the alar canal (alisphenoid canalof Gregory, 1910) and then into the orbit viathe rostral alar foramen. The other principaloccupant of the alar canal, the maxillaryartery, has a course wholly outside the cranialcavity. It enters the caudal opening of thealar canal on the basicranium, in the base ofthe temporal wing of the basisphenoid (ali-sphenoid), anterior to the foramen ovale, andenters the orbit with the maxillary nerve.Within the orbit, the maxillary artery sup-plies the external ophthalmic artery. Betweenthe orbital fissure and the rostral alarforamen, a small foramen alare parvum may


be present, transmitting the zygomatic nervefrom the alar canal to the orbit.

In the Pteropus fetus, there is a singleforamen of exit for the various structurespassing through the orbital fissure, foramenrotundum, and alar canal of the dog. Thisaperture, which we term the sphenorbitalfissure (fissura sphenorbitalis) as in Gregory(1910) but also including the foramen rotun-dum, is between the alisphenoid, orbito-sphenoid, the cartilaginous central stembetween the pre- and basisphenoid ossifica-tions, pterygoid, and palatine. It transmitstwo distinct bundles of structures within theirrespective connective tissue sheaths from thecavum epiptericum to the back of the orbit.Superiorly are the oculomotor, trochlear,ophthalmic (V1), and abducens nerves, theexternal ophthalmic artery or ramus orbitalis(sensu Wible, 1987), and the ophthalmicvenous plexus. Inferiorly are the maxillarynerve (V2), the maxillary artery or ramusinfraorbitalis (sensu Wible, 1987), and ac-companying veins. The maxillary arteryenters the cavum epiptericum via the foramenovale, and during its intracranial coursesends off the external ophthalmic artery.The Pteropus fetus is further distinguishedfrom the dog by the position of the pter-ygopalatine ganglion on the maxillarynerve; in the dog it lies within the orbit, wellanterior to the rostral opening of the alarcanal, but in the bat it is within the cavumepiptericum.

In Pteropus lylei CM 87972, the largesphenorbital fissure is between the alisphe-noid, orbitosphenoid, and pterygoid, with thepalatine nearly contributing to its floor(fig. 11). On the right side of CM 87972and bilaterally in CM 87973, the alisphenoidforming the lateral wall of the sphenorbitalfissure has a distinct medial process thatpartially divides that opening into superiorand inferior halves. This partial divisionreflects the situation in the fetus, with itsdistinct superior and inferior bundles.

In summary, Pteropus has a single opening(sphenorbital fissure) that serves the functionof the orbital fissure, foramen rotundum,rostral alar foramen, and foramen alareparvum of the dog. Additionally, two struc-tures present in the orbit in the dog arepresent in the cavum epiptericum of Pter-

opus: the external ophthalmic artery and thepterygopalatine ganglion (ganglion pterygo-palatinum).

STYLOMASTOID FORAMEN: In the dog(Evans, 1993), the stylomastoid foramen(foramen stylomastoideum) is the openingthat transmits the facial nerve from themiddle ear to the posterolateral surface ofthe auditory bulla. It is in the posterolateralaspect of the auditory bulla entirely withinthe petrous temporal (petrosal) and is alsooccupied by the stylomastoid artery (arteriastylomastoidea, sometimes double) off theposterior (caudal) auricular artery. In thePteropus fetus, the facial nerve leaves themiddle ear via a gap between the cartilagi-nous tympanohyoid laterally and ventrallyand the m. stapedius medially. Also trans-mitted is a small artery to the m. stapediusfrom the posterior auricular artery. In P. lyleiCM 87973 and P. livingstonii AMNH274477, the exit of the facial nerve is thestylomastoid notch (fig. 13). Flooring thenotch is the ossified tympanohyoid, andforming the lateral wall is the crest thatrepresents the posterior continuation of thecrista parotica (De Beer, 1937), the lateralsection of the caudal tympanic process of thepetrosal (MacPhee, 1981).

STAPEDIAL ARTERY: In extant placen-tals, three major paired arteries supply bloodto the adult head: the internal carotid (arteriacarotis interna) and the vertebral artery(arteria vertebralis) supply the brain, andthe external carotid (arteria carotis externa)supplies extracranial soft tissues (Tandler,1899, 1901). During development, anothermajor paired artery, the stapedial artery(arteria stapedia) off the internal carotid,forms and sends branches that accompanythe three divisions of the trigeminal nerve(Tandler, 1902; Wible, 1984, 1987). However,over the course of development in manyplacentals, including megachiropterans, thestapedial artery involutes, and most or all ofits end branches are annexed to the externalcarotid system (Tandler, 1899, 1901; Bugge,1974, 1978, 1979; Wible, 1984, 1987). Whenpresent, the placental stapedial artery oftenruns on the back of the promontorium of thepetrosal in a groove directed at the fenestravestibuli (Wible, 1987) and invariably passesthrough the intracrural foramen of the stapes


(Novacek and Wyss, 1986; Wible, 1987).Beyond the stapes, in the embryonic pattern,the stapedial artery has two major branches:the ramus superior and ramus inferior(Tandler, 1902; Wible, 1984, 1987). The bulkof the course of the ramus superior is withinthe cranial cavity, where it divides into ananterior division that enters the orbit tosupply the ramus supraorbitalis accompany-ing the branches of the ophthalmic nerve anda posterior division that supplies temporalrami into the temporal fossa and an arteriadiploetica magna that reaches the occiput. Incontrast, the bulk of the course of the ramusinferior is extracranial; its principal endbranches are the ramus infraorbitalis andramus mandibularis, which accompanybranches of the maxillary and mandibularnerves, respectively.

To date, the cranial arterial pattern hasbeen studied in only three adult megachir-opterans: Pteropus vampyrus (5 P. edulis)(Tandler, 1899) and Rousettus aegyptiacusand Rousettus sp. (5 Cynonycteris aegyptiacaand Cynonycteris sp.) (Grosser, 1901). In allthree, the main stem of the stapedial artery islacking and the end branches of the stapedialartery are annexed to the external carotidsystem via the maxillary artery. The ramusinferior arises from the maxillary arterybehind the foramen ovale, runs posteriorlyinto the middle ear, and supplies the mainstem of the ramus superior. The ramussuperior ends endocranially and does notreach the orbit; Grosser (1901) reportedtemporal rami of the ramus superior, butTandler (1899) did not. Beyond the origin ofthe ramus inferior, the maxillary artery (5ramus infraorbitalis) follows an unusualcourse through the cranial cavity, enteringwith the mandibular nerve and exiting withthe maxillary nerve.

The Pteropus fetus studied here showsessentially the same pattern (see also recon-structions in Wible, 1992: figs. 1, 2). Howev-er, our study of serial sections providessignificantly more detail than the accountsby Tandler (1899) and Grosser (1901). In thefetus, the ramus inferior of the stapedialartery arises from the maxillary artery poster-oventral to the foramen ovale. It runsposteriorly beneath the alisphenoid lateralto the otic ganglion (fig. 33), which extends

into the front of the middle ear. At the backof the alisphenoid, the ramus inferior movesinto a fissure between the epitympanic wingof the parietal dorsally and the squamosalventrolaterally; this fissure is open ventrome-dially, dorsal to the plane of the tympanicroof, as defined by the tegmen tympani.Within this fissure, the ramus inferior isjoined by an artery that runs dorsally into thecranial cavity through a foramen in theventromedial aspect of the parietal (fig. 34).This artery, the anterior division of the ramussuperior, runs anterodorsally along the en-docranial surface of the parietal (fig. 33) andends between the parietal and the back of thecartilaginous ala orbitalis, the precursor ofthe orbitosphenoid. The artery formed at thejunction of the ramus inferior and anteriordivision of the ramus superior continuesposteriorly in a deep sulcus in the ventralsurface of the parietal; ventrolateral to thissulcus is the squamosal and ventromedial isa space above the tegmen tympani androstral entotympanic, which is occupiedmedially by the lesser petrosal nerve (nervuspetrosus minus). After a short course, thisartery divides into a smaller stapedial arterythat moves posteromedially toward the mid-dle ear and a larger posterior division of theramus superior that moves posterodorsolat-erally, still within a deep sulcus in the parietalthat is floored ventrolaterally by the squa-mosal (fig. 35). The stapedial artery runs inthe gap between the tegmen tympani and thepars cochlearis of the petrosal and disappearsbeneath the secondary facial foramen, farfrom its embryonic origin from the internalcarotid artery. The posterior division of theramus superior runs dorsal to the capsulo-parietal emissary vein as it enters thesquamosal and provides the first of two ramitemporales, which run dorsolaterally betweenthe parietal and squamosal into the m.temporalis. After the origin of the first ramustemporalis, the posterior division continuesposteriorly between the parietal medially andsquamosal laterally. The second ramus tem-poralis is sent off over the fossa incudis, andthe small posterior division continues as thearteria diploetica magna a short distance intothe posttemporal canal between the parietal,squamosal, and pars canalicularis of theauditory capsule.


VASCULAR FORAMEN OF THE LACRI-

MAL: In addition to the lacrimal foramen,CM 87972 (and the other specimens ofPteropus lylei examined in this study) hasa small foramen in the orbital process of thelacrimal (between the lacrimal and maxilla onthe right side) that leads into a canal openingin the posterior floor of the lacrimal foramen(fig. 12), termed here the vascular foramen ofthe lacrimal. In CM 87973, this foramen isdouble on the left side. Based on the Pteropusfetus, this foramen transmits an artery andvein into the lacrimal canal; these vesselsoriginate from the infraorbital vessels priorto their entrance into the maxillary foramen.

DENTITION

The dental formula in Pteropus lylei is I2/2,C1/1, P3/3, M2/3. Homologies of incisor andpremolar teeth in bats have been the sourceof debate for the last century (e.g., Miller,1907; Andersen, 1912; Handley, 1959;Slaughter, 1970; Thenius, 1989). We followAndersen (1912) in adopting the followingnomenclature for the teeth in Pteropus: in theupper dentition, the incisors are assumed torepresent I1 and I2, the premolars P1, P3,and P4, and the molars M1 and M2.Similarly, the lower dentition is assumed toinclude i1, i2, p1, p3, p4, m1, m2, and m3.The dental nomenclature used here includesthe following terms: upper and lower toothrows (arcus dentalis superior et inferior),permanent teeth (dentes permanentes), de-ciduous teeth (dentis decidui), incisor teeth(dentes incisivi), canine teeth (dentes canini),premolar teeth (dentes praemolares), molarteeth (dentes molares), crown (corona dentis),shaft (5 neck; collum dentis), root (radixdentis), cusp or cuspule (cuspis dentis), cingu-lum, tip of tooth or cusp (apex cuspidis),occlusal surface (facies occlusalis), lateral (5vestibular, 5 buccal, 5 labial) surface (faciesvestibularis, facies labialis), and medial (5lingual) surface (facies lingualis). Homologyof cusps with respect to a typical tribosphenicmolar is discussed in Comparisons: Dentition.

PERMANENT DENTITION

None of the individuals examined for thisstudy exhibited anomalies in dental formulae

other than those that can be attributed to ageand tooth wear. Anomalies in dental formu-lae appear to be rare in Pteropus; Andersen(1912) examined over 600 skulls of Pteropusbut found aberrations in dental formulae inonly 10 individuals (less than 2%). All of theanomalies noted by Andersen (1912) werefound in individuals referred to Pteropusgiganteus, P. vampyrus, or P. scapulatus,including: (1) presence of a well-developedi3 on both sides in one individual; (2)presence of a supernumerary p2 in the broaddiastema between p1 and p3 on one side inone individual; (3) presence of a supernumer-ary premolar between p3 and p4 on bothsides in one individual; (4) absence of m3(and its alveolus) on both sides in fiveindividuals and on one side in another; (5)absence of m2 on one side in one individual(which also lacked m3); (6) presence of a m4on one side in one individual; and (7)presence of M3 on both sides in one in-dividual.

UPPER INCISORS: The upper incisors ofPteropus lylei are blunt and somewhatspatulate, with the crown distinct from theshaft (fig. 4). Neither I1 nor I2 has a poster-obasal cingulum. Adjacent upper incisors areseparated by small diastemata, and do notcontact one another at either crown oralveolus. The crowns of opposing right andleft I1 converge ventromedially but theseteeth never approach contact with oneanother, even in young animals with unwornteeth (fig. 4). I2 is separated from the uppercanine by a large diastema. I1 and I2 aresubequal in height, but I1 projects furtherventrally as a result of the more ventralposition of its alveolus on the premaxilla. Thecrown of I1 is broader than the crown of I2.The relative proportions of these teeth varywith tooth wear, but the width of I1 neverexceeds 1.25 times the width of I2. The crownof I1 is slightly asymmetrical, achieving itsgreatest height and breadth medial to thelong axis of the tooth. This asymmetry ismost obvious in unworn teeth and maybecome somewhat obscured when tooth wearreduces crown height. Faint traces of twocusps are visible on the tip of the crown of I1in some unworn dentitions (e.g., AMNH237598), with the medial cusp the larger ofthe two. Only one cusp is ever visible on I2.


This cusp is centrally located and gives I2a somewhat more pointed appearance thanI1.

In old individuals, the crowns of both I1and I2 may wear completely away, leavingthese teeth as flat-topped pegs. Wear isusually greatest on I1 because this toothprojects further ventrally than I2, and erosionof the crown of I1 may be complete beforethe crown of I2 is completely ablated. In oneextremely old individual (AMNH 217045;fig. 38B), both right and left I1 have beenbroken off at their bases, but the root andalveolus of each tooth remains clearly distinct(unlike those of missing molar teeth, whichare grown over with bone). I2 in thisindividual remains on both sides as a peglikestub.

UPPER CANINE: The upper canine ofPteropus lylei is long, slender, and gentlyrecurved (fig. 4, 36). The right and leftcanines are slightly divergent, such that thetip of each tooth lies directly ventral to theouter edge of its alveolus in relatively unworndentitions. The length (5 crown height) of

the canine is approximately equal to theheight of the nasal process of the premaxilla,and canine length is greater than the height ofthe rostrum above the canine alveolus inyoung animals with unworn teeth. The tip ofthe canine tapers to a relatively sharp pointwhen unworn, but rapidly wears to a bluntpoint in older individuals. A narrow basalcingulum forms a continuous rim around theposterior and medial base of the canine. Insome individuals with unworn teeth (e.g.,AMNH 237598), the edge of the cingulum ismarked by traces of several small cuspules.The anterior face of the crown of the canineis marked by a deep and broad verticalgroove that runs from the base of the crownto nearly the tip of the tooth (fig. 4). Breadthof the groove is greatest near the base, andthe groove narrows and becomes moreshallow as it approaches the tip of the tooth.The posteromedial surface of the tooth ismarked by a keel-like ridge that runs fromthe base of the tooth (just inside the basalcingulum) to almost the tip of the tooth(fig. 36). This ridge forms the medial

Fig. 36. Pteropus lylei AMNH 237595, ventrolateral view of the permanent upper dentition and hardpalate. Scale 5 5 mm. Abbreviations: C upper canine; I1 first upper incisor; I2 second upper incisor; lclateral cusp of cheek teeth; M1 first upper molar; M2 second upper molar; mapf major palatine foramen;mc medial cusp of cheek teeth; mx maxilla; P1 first upper premolar; P3 third upper premolar; P4 fourthupper premolar; pal palatine; pmx premaxilla; rc posteromedial ridge of upper canine.


boundary of the posterior face of the tooth,which is broadly concave and runs roughlyparallel to the groove on the anterior face ofthe tooth. The lateral face of the tooth isgently convex, and the medial surface is flat.The canine is roughly rectangular in crosssection throughout most of its length, withthe two long edges corresponding to themedial and lateral faces of the tooth, and theshorter edges corresponding to the anteriorand posterior faces.

Wear on the canine apparently continuesthroughout life, often beginning before toothwear is apparent elsewhere in the dentition.Young adults generally exhibit at least somewear on the tip of the canine. As wearprogresses, the basal cingulum becomesobscured, and a large wear facet forms downthe posteromedial face of the tooth, obscur-ing the keel-like ridge. Wear reaches itsextreme in very old individuals, in whichthe canine has been worn down to a flat-topped, mushroom-shaped peg (fig. 38B).The canines in most museum specimens have

a single large vertical crack running from thetip to the base of the crown, but these cracksare apparently postmortem artifacts of thepreparation process.

UPPER PREMOLARS: The upper premo-lar dentition of Pteropus lylei consists of threeteeth: a tiny P1, and a large P3 and P4. TheP1 is not deciduous but is often absent on oneor both sides in older adults. P1 is a tiny,styliform tooth with an undifferentiatedcrown that tapers to a blunt point (fig. 36).P1 has a single root, and its alveolus typicallylies just posterior to the alveolus for thecanine. In some young individuals, the P1alveolus is partially confluent with the caninealveolus, but these alveoli are separate inmost adults. Skull growth appears to affectthe relative position of the P1, as the size ofthe diastema between the canine and P1alveoli tends to be greater in older, largeranimals. In one of the oldest individuals inour sample (AMNH 30217), the remnant ofthe empty alveolus for P1 lies midwaybetween the canine and P3 on both sides of

Fig. 37. Pteropus lylei AMNH 237595, dorsocaudolateral view of the mandible showing permanentlower dentition. Scale 5 5 mm. Abbreviations: c canine; i1 first lower incisor; i2 second lower incisor; lclateral cusp of cheek teeth; m1 first lower molar; m2 second lower molar; m3 third lower molar; manfmandibular foramen; mc medial cusp of cheek teeth; p1 first lower premolar; p3 third lower premolar; p4fourth lower premolar.


the skull. Comparisons among skulls revealthat the distance between P1 and P3 varieslittle with age, suggesting that differentialgrowth occurs in the skull in the regionbetween the canine and P1. Because P1 is sosmall, the functional cheek tooth row consistsof four teeth: the two posterior premolars (P3and P4) and the two molars (M1 and M2).These teeth are always separated from thecanine by a large diastema, and are separatedfrom each other by very small diastematathat prevent adjacent tooth crowns fromtouching one another.

The posterior upper premolars (P3 and P4)are large, double-rooted teeth with crownlengths slightly shorter than M1 (fig. 36). Asin other Pteropus species, crown heightdecreases from anterior to posterior alongthe cheek tooth row (P3–M2), so P3 is thelargest of the cheek teeth in lateral view. BothP3 and P4 have a large lateral cusp anda smaller medial cusp. The cusps on eachtooth consist of longitudinal ridges that areincompletely separated at their bases bya median groove (fig. 36). The median grooveterminates posteriorly in a small basinbounded by a weakly developed posterobasalledge, which forms a narrow rim around theback of the tooth. Traces of small cuspulescan occasionally be seen along the poster-obasal rim.

The crown of P3 is slightly higher than it islong. The anterior edge of the tooth is convexand the posterior edge is concave, so thetooth appears slightly recurved in lateralview. The main bulk of the tooth is centeredover the anterior root, with the tips of bothcusps offset anteriorly from the midpoint ofthe tooth. The occlusal outline of P3 is ovalto subrectangular. The large lateral cusp isroughly triangular in cross section, witha medial ridge that connects it to the lowermedial cusp across the median groove. Theanteroposterior length of the medial cusp issomewhat smaller than that of the lateralcusp. The posterobasal rim is very low on P3(fig. 36).

Crown height of P4 is markedly less thanthat of P3, and both cusps on P4 have lower,more rounded tips than their counterparts onP3 (fig. 36). The posterior edge of the lateralcusp of P4 is either straight or very slightlyconvex, so the tooth does not appear re-

curved in lateral view. P4 is always subrec-tangular in occlusal view, and is somewhatbroader posteriorly than P3. The poster-obasal rim is also higher on P4 than on P3,giving the posterior portion of P4 a molari-form appearance. Indeed, overall morpholo-gy of P4 is intermediate between that of P3and M1.

Wear on the large premolars (P3 and P4)typically occurs on the ventromedial aspectof the cusps. Although the lateral cusps arehigher than the medial cusps, the degree ofwear is typically similar on both cusps,suggesting that abrasion occurs on bothcusps simultaneously during feeding. Wearmay progress until the entire surface of thecrown is worn away (e.g., AMNH 30217;fig. 38A), and some very old individuals maylose the cheek teeth altogether (e.g., AMNH217045; fig. 38B). In older individuals, theplane of tooth wear is obvious across theentire cheek tooth dentition. The wear planeis oriented such that wear is greatest poster-iorly and medially on both individual teethand on the dentition as a whole.

UPPER MOLARS: The upper molar den-tition of Pteropus lylei consists of twodouble-rooted teeth: a large M1 and a smallM2. The M1 has the longest crown length ofany tooth in the upper dentition, and it isonly slightly narrower than P4. The M2 ismuch smaller, less than half the length of M1and markedly narrower than all of the othercheek teeth except P1 (fig. 36).

The M1 is subrectangular in occlusaloutline, with the posterior end of the toothmore rounded in outline than the anteriorend (fig. 3). Like the premolars, the crown ofM1 is marked by a median groove that isflanked by two ridges, each of which rises toform a cusp near the anterior limit of thetooth. The lateral cusp is slightly higher thanthe medial cusp. The cusps are rounded andnot recurved. Posteriorly, each cusp iscontinuous with a posterobasal rim that runsaround the back of the tooth. In someindividuals, traces of a distinct posterolateralcusp can be seen. The basin is broad and iscontinuous with the median groove thatseparates the medial and lateral cusps.

The M2 is small and oval in occlusaloutline (fig. 3). Only one cusp is welldeveloped: a bulbous cusp on the anterolat-


eral edge of the tooth. The base of this cuspintrudes into an otherwise oval central basin(fig. 36). The basin is bounded laterally,posteriorly, and medially by a raised rim thatis not continuous with the anterolateral cusp.This raised rim is separated from the cusp byshallow notches anteriorly and laterally. Insome individuals with unworn teeth (e.g.,AMNH 237598), a tiny cusp is developed onthe posterolateral corner of the rim. None ofthe cusps or ridges on M2 are very high, sothe crown of the tooth appears relatively flatin lateral view. The occlusal surface of M2lies in roughly the same plane as the posteriorhalf of M1.

As noted above under the discussion ofpremolars, wear on the cheek teeth occursalong an oblique plane that is oriented suchthat wear is greatest posteriorly and mediallyon both individual teeth and on the dentitionas a whole. Accordingly, M2 typicallyexhibits greater wear than M1, and M1

exhibits greater wear than the premolars.Wear may progress until the entire surface ofthe crown of each molar tooth is worn away(e.g., AMNH 30217; fig. 38A), and some veryold individuals may lose these teeth altogeth-er (e.g., AMNH 217045; fig. 38B). As theupper cheek teeth are worn down to nubs, itseems likely that they are lost progressivelybeginning at the back of the tooth row, wherewear is greatest. This seems confirmed byexamination of AMNH 217045, which lacksP3–M2 on both sides (fig. 38B). In thisindividual, the alveoli of the molar teeth arecompletely overgrown with spongy bone. TheP4 alveoli are largely overgrown, and thoseof P3 are still visible, with the broken anteriorroot of P3 still present on one side.

LOWER INCISORS: The lower incisors ofPteropus lylei are markedly smaller than theupper incisors. The i2 is roughly twice the sizeof i1 in crown breadth, crown height, andcross-sectional area, but the height of the tipof i1 above the alveolar line is only slightlyless than that of i2 due to differences in rootlength and the relative placement of thealveoli (fig. 8). Right and left i1 are separatedby a median diastema, and these teeth aresomewhat divergent (i.e., the shaft of eachtooth is directed dorsally and slightly later-ally). The i1, i2, and canine on each side ofthe jaw are placed close together (with noobvious diastemata), but adjacent toothcrowns do not contact one another.

Both i1 and i2 have a circular cross sectionwhen seen in occlusal (dorsal) view (fig. 7).The i1 is a peglike tooth that has a crownonly slightly differentiated from the root. Inrelatively unworn dentitions, traces of a singlecusp can be seen centered on the crown. Incontrast, i2 shows clear evidence of two cuspsin younger animals. These cusps are orientedside by side, parallel to the anterior face ofthe tooth. Crown development is much morepronounced in i2 than in i1, with the crownof i2 clearly distinct from the shaft of theroot.

Wear begins very early on the incisors, anddistinct wear facets can be seen on both i1and i2 even in relatively young adults. Wearoccurs on the anterodorsal surface of eachtooth. In older individuals, a distinct wearplane forms across the entire lower incisordentition; this plane runs obliquely from

Fig. 38. Pteropus lylei, tooth wear of upperdentition in AMNH 30217 (A) and AMNH217045 (B). Scale 5 5 mm.


posterodorsal to anteroventral, so that theflat wear facet on each tooth is directedanterodorsally. As wear progresses, thecrowns of the incisors are worn away toleave these teeth as flat-topped pegs. In veryold individuals, some or all of the lowerincisors may be lost and their alveoli filledwith spongy bone (e.g., AMNH 217045,which lacks both left lower incisors).

LOWER CANINE: The lower canines ofPteropus lylei are somewhat shorter, moreslender, more strongly recurved, and moredivergent than the upper canines (figs. 8, 37).Unlike the upper canines, which are approx-imately the same size in both sexes, there isconsiderable sexual dimorphism in the lowercanines, which are markedly longer in malesthan in females. In females with minimaltooth wear, the height of the canine isapproximately equal to the depth of theramus of the mandible; in males, canineheight exceeds depth of the ramus. The tip ofthe canine tapers to a relatively sharp pointwhen unworn, but wears to a blunt point inolder individuals. A poorly developed basalcingulum forms a continuous rim around theposterior and medial base of the canine. Insome individuals with unworn teeth (e.g.,AMNH 237598), the edge of the cingulummay be marked by traces of several smallcuspules.

The anterior (fig. 8) and lateral (fig. 6)faces of the lower canine typically forma smoothly curving convex surface aroundthe tooth. There is no anterior groove on thelower canine. However, in some individuals(e.g., AMNH 240005), the anterior andlateral surfaces are each relatively flat,meeting at a poorly developed ridge thatruns from the tooth base to the tip along theanteromedial aspect of the tooth. The poster-omedial surface of the tooth is marked bya keel-like ridge that runs from the base ofthe tooth (just inside the basal cingulum) toalmost the tip of the tooth (fig. 37). This ridgeforms the medial boundary of the posteriorface of the tooth (which is flat or slightlyconcave), and the posterior boundary of themedial face of the tooth (which is flat). Thelateral face of the tooth is gently convex, andthe medial surface is flat.

Wear on the lower canine appears toproceed at a slower rate than wear on the

upper canine. Most adults show some wear atthe tip of the tooth, but large wear facets areuncommon until very late in the life of theanimal. When a wear facet does form, itwraps around the posterior and medialsurfaces of the tooth, eventually extendingaround the anterior face of the tooth to leaveonly the lateral surface of the enamel intact(e.g., AMNH 30217). The canine remainspointed even as the tooth wears away,becoming more conical as the wear facetdevelops. Wear reaches its extreme in veryold individuals, in which the canine has beenworn down to a flat-topped peg (e.g.,AMNH 217045).

LOWER PREMOLARS: The lower premo-lar dentition of Pteropus lylei consists of threeteeth: a small p1, and a large p3 and p4(figs. 6, 7, 37). Although relatively small, p1 ismuch larger than P1, and it is also notdeciduous like the latter. The p1 is singlerooted and is approximately twice the size ofi2. The crown is oval and relatively flat, witha very shallow central depression. In younganimals, the lateral edge may be slightlyhigher than the medial edge of p1, and tracesof two cusps may be seen along the lateralborder of the tooth. The p1 is separated fromthe lower canine by a small diastema(somewhat less than the diameter of thecrown of p1), and from the crown of p3 bya diastema that is the same size or somewhatlarger. Wear on p1 is not evident until late inlife, when wear on the anterior dentitionreduces the distance between the upper andlower jaws during occlusion, bringing theposteromedial surface of the upper canineinto contact with the lateral surface of p1.This occlusal contact produces a distinctwear facet on p1 in older adults (e.g., AMNH30217). Like the other cheek teeth, p1eventually wears down to become a flat-topped peg in very old animals (e.g., AMNH217045).

The posterior lower premolars (p3 and p4)are large, double-rooted teeth with crownlengths approximately equal to that of m1.The morphology of these teeth is very similarto that of their upper counterparts (cf. figs. 36and 37). As in the upper dentition, crownheight decreases from anterior to posterioralong the cheek tooth row (p3 to m3), so p3 isthe largest of the cheek teeth in lateral view


(fig. 37). Both p3 and p4 have a large lateralcusp and a smaller medial cusp. The crown ofp3 is slightly higher than it is long, and themain bulk of the tooth is centered over theanterior root, with the tip of the lateral cuspoffset anteriorly from the midpoint of thetooth. The anterior edge of the tooth isconvex and the posterior edge is concave, sothe tooth appears recurved in lateral view.The occlusal outline of p3 is subrectangular(fig. 7). The large lateral cusp is roughlytriangular in cross section, with a medialridge that connects it to the lower medialcusp (fig. 37). There is no median groove onp3, just a small notch that separates the two

cusps. The degree of differentiation of themedial cusp is variable; in many individuals,it is clearly present and distinct from thelateral cusp (e.g., AMNH 237598), whereasin other specimens the medial cusp is barelyvisible (e.g., AMNH 237599). Posteriorly,a smooth, slightly concave surface runs fromthe medial ridge to the back of the tooth, andthere is no posterior basin. The posterobasalrim is very low, and traces of small cuspulescan occasionally be seen along its edge.

The morphology of p4 is nearly identicalto that of P4 (cf. figs. 36 and 37). The crownheight of p4 is markedly less than that of p3,and the lateral cusp on p4 has a lower, more

Fig. 39. Pteropus lylei AMNH 237595, lateral view of the rostrum and occluding mandible showingpattern of occlusion in the permanent dentition. Scale 5 5 mm. Abbreviations: ac alveolar canal; C uppercanine; c lower canine; Cju upper canine jugum; I1 first upper incisor; i1 first lower incisor; I2 second upperincisor; i2 second lower incisor; ioc infraorbital canal; M1 first upper molar; m1 first lower molar; M2second upper molar; m2 second lower molar; m3 third lower molar; P1 first upper premolar; p1 first lowerpremolar; P3 third upper premolar; p3 third lower premolar; P4 fourth upper premolar; p4 fourthlower premolar.


rounded tip than its counterpart on p3. Theposterior edge of the lateral cusp of p4 iseither straight or somewhat convex, so thetooth does not appear recurved in lateralview. The p4 is always subrectangular inocclusal view, and is approximately the samewidth as p3. The cusps on p4 consist oflongitudinal ridges that are incompletelyseparated at their bases by a median groove.The median groove terminates posteriorly ina small basin bounded by a weakly developedposterobasal ledge, which forms a narrowrim around the back of the tooth. Traces ofsmall cuspules can sometimes be seen alongthe posterobasal rim.

Wear of p3 and p4 is typically confined tothe tips of the cusps until old age, with muchgreater wear occurring on the lateral cuspthan on the medial cusp. In old individuals(e.g., AMNH 30217), a large wear facet maydevelop on the posterolateral aspect of themain cusp on p3 where it comes in contactwith P3. A smaller wear facet may alsodevelop on the anterior side of the main cuspon p4 where it contacts the posterior portionof the lateral cusp of P3 during chewing.Contact between upper and lower premolarsis precluded in younger adults by priorocclusion of the anterior dentition. Nocontact seems to occur between p4 and P4

Fig. 40. Pteropus hypomelanus luteus AMNH 159084, ventrolateral view of the upper deciduousdentition. Scale 5 5 mm. Abbreviations: C permanent upper canine; Cju upper canine jugum; dCdeciduous upper canine; dI1 deciduous first upper incisor; dI2 deciduous second upper incisor; dP1deciduous first upper premolar; dP2 deciduous second upper premolar; I1 permanent first upper incisor;M1 permanent first upper molar; mx maxilla; P1 permanent first upper premolar; P3 permanent thirdupper premolar; P4 permanent fourth upper premolar; pmx premaxilla.


at any age. Wear on the cheek teeth mayprogress until the entire surface of the crownis worn away (e.g., p4 in AMNH 30217), andsome very old individuals may lose the cheekteeth altogether (e.g., AMNH 217045). Inolder individuals, a continuous, slightlyconvex plane of tooth wear occurs acrossp4–m3. The wear plane is oriented such thatwear is greatest posteriorly, so teeth in theback of the cheek tooth dentition showgreater wear than those in the front.

LOWER MOLARS: The lower molar den-tition of Pteropus lylei consists of three teeth:a large m1 and m2, and a small m3 (figs. 6, 7,37). Crown lengths of m1 and m2 are similar,and both teeth are double rooted andsubrectangular in occlusal outline. The m3is much smaller, with a crown that is almostcircular in occlusal view. The m3 is approx-imately the same size as p1 and is singlerooted, although the roots may be partially

divided inside the jaw. The m1 and m2 lie inline with the posterior premolars; in contrast,m3 is slightly offset toward the medial side ofthe ramus of the mandible.

The morphology of m1 is very similar tothat of its upper counterpart (cf. figs. 36 and37). The crown of m1 is marked by a mediangroove that is flanked by two ridges, each ofwhich rises to form a cusp near the anteriorlimit of the tooth (fig. 37). The lateral cusp isslightly higher than the medial cusp, andboth are rounded and not recurved. Themedial cusp in some young adults (e.g.,AMNH 237598) can be seen to be composedof two adjacent cusps that are distinct only attheir tips. However, only a single, somewhatelongate medial cusp is distinct on m1 inmost individuals. Posteriorly, each cusp iscontinuous with a posterobasal rim that runsaround the back of the tooth. The basindefined by this rim is continuous with the

Fig. 41. Pteropus hypomelanus luteus AMNH 159082, dorsocaudolateral view of the mandible showingthe deciduous lower dentition. Scale 5 5 mm. Abbreviations: c permanent lower canine; dc deciduouslower canine; di1 deciduous first lower incisor; di2 deciduous second lower incisor; dp1 deciduous firstlower premolar; dp2 deciduous second lower premolar; m1 permanent first lower molar; m2 permanentsecond lower molar; p1 permanent first lower premolar; p3 permanent third lower premolar; p4 permanentfourth lower premolar.


median groove that separates the medial andlateral cusps. Because the posterobasal rim isvery weakly developed across the back end ofthe tooth, the basin appears open posteriorlyin most individuals.

The m2 is somewhat smaller than m1 inboth length and height, but is approximatelythe same width (fig. 37). Only the lateral cuspis developed, and it is low and rounded. Themedial groove is broad and shallow, forminga central basin that runs from the anterome-dial portion of the tooth (medial to the cusp)to the posterior of the tooth. A raised rimwith no distinct cusps surrounds the centralbasin anteriorly, medially, and posteriorly,and terminates at a notch on the lateral edgeof the tooth just posterior to the cusp. Themedial portion of the ridge is roughlyhorizontal.

The m3 is small and nearly round inocclusal outline (fig. 7). It is approximatelythe same size as p1. Only one cusp isdeveloped on m3: a bulbous cusp on theanterolateral edge of the tooth (fig. 37). Thecenter of the occlusal surface of the tooth is

marked by a slight depression, but there is noclear definition of a rim. The crown of thetooth appears relatively flat in lateral view.

No contact seems to occur between theupper and lower molars at any age. Never-theless, wear on the molar teeth may progressuntil the entire surface of the crown of eachtooth is worn away (e.g., AMNH 30217), andsome very old individuals may lose most ofthe lower molars (e.g., AMNH 217045, whichretains only the roots of the left m2 and oneroot of the right m1). In older individuals,a continuous, slightly convex plane of toothwear occurs across p4–m3. The wear plane isoriented such that wear is greatest poster-iorly, so teeth in the back of the cheek toothdentition show greater wear than those in thefront.

OCCLUSION: As in other members ofPteropus, in P. lylei occlusion is controlledby the anterior dentition (see fig. 39). Whenthe mandible is centered and the mouthclosed, the only teeth in direct contact areeither the upper and lower canines or theupper and lower incisors, depending upon the

Fig. 42. Pteropus hypomelanus luteus AMNH 159082, rostral view of the mandible showing thedeciduous dentition. Scale 5 5 mm. Abbreviation: amf anterior mental foramen; c permanent lowercanine; dc deciduous lower canine; di1 deciduous first lower incisor; di2 deciduous second lower incisor;dp1 deciduous first lower premolar; mas mandibular symphysis; pmf posterior mental foramen.


position of the mandible. When the mandibleis thrust forward, the incisors occlude; whenit is retracted, the canines occlude. When themouth is closed, the crowns of the lowerincisors fit in behind those of the upperincisors, and the lower canine fits in front ofthe upper canine. The lower first premolar(p1) opposes the posteromedial ridge on theupper canine but does not occlude with it inyounger adults due to prior occlusion of thecanines and incisors. However, as wearreduces crown height of the anterior teethin older adults, p1 approaches the uppercanine and subsequently begins to occludewith the posteromedial ridge.

The upper and lower cheek teeth aregenerally not in contact when the jaw iscentered and at rest. The main cusps of thelower teeth fit in front of and slightly medialto their counterparts in the upper dentition,alternating like the teeth on a pair of pinkingshears (fig. 39). Accordingly, the main cuspof p3 fits into the diastema between P1 andP3. The main cusp of p4 fits into theposterior basin on P3, just anterior to thecusps on P4 and posterior to the cusps on P3.Subsequent teeth maintain this pattern,although reduction in cusp height on therear teeth (M2, m2, and m3) reduces thedegree to which opposing teeth interlock. TheM2, which has a relatively flat crown, lies inopposition to the anterior half of the crownof m3 and the posterior half of the crown ofm2. The m3 is the most posterior tooth in thedentition when the jaws are closed. Althoughall cheek teeth exhibit considerable wear inolder adults, there is no evidence that upperand lower molars ever contact one another.However, some contact does occur betweenP3 and p3, and P3 and p4, in old adults whenwear is advanced in the anterior dentition.

DECIDUOUS DENTITION

We examined the deciduous dentition injuvenile skulls of four specimens of Pteropushypomelanus luteus (AMNH 159082–159085). The upper deciduous dentitionconsists of two incisors, a canine, and twodeciduous premolars (Leche, 1876–1877;fig. 40). All are simple spicules. The de-ciduous incisors and canine are markedlyrecurved and are always implanted so that

Fig. 43. Caudal view of the occiput of the pupof Pteropus capistratus AMNH 194276 (A) and theyoung adult of Pteropus lylei CM 87972 (B), andcaudodorsal view of the skull of P. lylei AMNH217045 (C). Scales 5 5 mm. Abbreviations: chochoanae; ec ectotympanic; eo exoccipital; frtforamina for rami temporales; gf glenoid fossa;ioc infraorbital canal; ip interparietal; me mastoidexposure of petrosal; nuc nuchal crest; oc occipitalcondyle; pa parietal; pcp paracondylar process; pgppostglenoid process; pop postorbital process; sosupraoccipital; tl temporal line.


the tips are directed posteriorly (fig. 40). Thedeciduous premolars are slightly recurved atthe tip, but their orientation is irregular. Theanterior deciduous premolars are usuallyoriented vertically (e.g., AMNH 159083)but may project somewhat anteriorly (e.g.,AMNH 159082). The posterior deciduouspremolars are very small and may project inany direction, especially when displaced byeruption of the anterior molar (fig. 40).

The adult replacements for the deciduousdentition are typically visible in even theyoungest pups (fig. 40). I1 and I2 erupt withtheir crowns directly lingual to dI1 and dI2.The permanent canine erupts anterior andlingual to the deciduous canine. The de-ciduous premolars are located more poster-iorly and appear to be associated with thespaces between erupting permanent teeth.The anterior deciduous premolar lies betweenthe erupting P3 and P4, and the posteriordeciduous premolar lies between the eruptingP4 and M1. There is no deciduous toothassociated with P1 in any of the specimens weexamined, as is the rule in many mammals(e.g., the dog; Evans, 1993).

The lower deciduous dentition resemblesthe upper dentition in comprising twoincisors, a canine, and two premolars(fig. 41). However, the morphology of theseteeth differs somewhat from their uppercounterparts. The deciduous lower incisorsare both peglike and blunt, and are notrecurved (figs. 41, 42). The medial incisor(di1) is markedly smaller than the lateraltooth (di2) in both length and breadth(fig. 42). The lower deciduous canine resem-bles the upper dC, and is a relatively large,recurved tooth. The first of the two de-ciduous premolars is similarly recurved, butthe second deciduous premolar is more peg-like and blunt in form. They also differ intheir orientation: the anterior deciduous pre-molar projects dorsally and somewhat ante-riorly (although its tip is recurved and thuspoints slightly posteriorly); in contrast, theposterior deciduous premolar lies almosthorizontally in our specimens, with the crownpointed anteriorly.

Like their upper counterparts, the decidu-ous lower teeth occupy consistent positionswith respect to their erupting replacements(fig. 41). The permanent incisor teeth erupt

with their crowns directly lingual to di1 anddi2. The permanent canine erupts anteriorand lingual to the deciduous canine. Theanterior deciduous premolar lies between theerupting p3 and p4, and the posterior de-ciduous premolar lies dorsal to the poster-olabial corner of the erupting p4. As in theupper dentition, there is no deciduous toothassociated with p1 in any of the specimens weexamined.

SKULL DEVELOPMENT

SHAPE CHANGE

AMNH 194276, a pup of Pteropus capis-tratus, is the youngest osteological specimenof Pteropus that we examined (see fig. 43A).As compared with adults of Pteropus of thehypomelanus type, the most striking featuresof this specimen are the very short rostrumand the large, rounded braincase. The orbit isalso very large, but this is typical of thetemminckii species group and is not generalfor Pteropus. The large jugum of the canineoccupies almost all of the space of the faciesfascialis of the maxilla in AMNH 194276. Incontrast, the jugum of the canine hasa definite rostral position in the adult.Therefore, during growth, the maxilla isapparently displaced rostrally and gains bonebetween the canine and the zygomatic pro-cess, presumably as the upper cheek teeth areadded to the tooth row in a rostrocaudalorder. This process of maxillary elongation isaccompanied by simultaneous elongation ofthe nasals, which, judging from the relativeposition of the canine juga, occurs chiefly inthe caudal half of the nasals. Likewise, thenasopharyngeal meatus and the palate expe-rience noticeable elongations during develop-ment.

At the same time that the rostrum isundergoing elongation, the frontal bones areremodeled such that a postorbital constric-tion (nonexistent in AMNH 194276) becomesapparent, clearly delineated by the temporallines (linea temporalis; fig. 43C). Relativedevelopment of these features varies greatlywithin Pteropus; as in larger species thepostorbital constriction is well marked(sometimes narrower than the interorbitalconstriction), and the temporal lines are so


Fig. 44. Sequence of bone fusion in the AMNH and CM series of Pteropus. Columns indicate the stageof bone fusion from 1 to 6, defined on the basis of a combination of tooth wear and selected osteologicaltraits (see text). Rows list sutures and synchondroses that are lost by fusion of their contributing bones, insuccessive order with respect to the age stages. From left to right, the first black cell for each suture or


well developed that they form a ridge overthe postorbital processes and join immedi-ately caudal to the processes into a sagittalcrest (crista sagittalis). In AMNH 194276, theposterior zygomatic root lies close to thebraincase and is oriented rostrally (fig. 43A).In adults, the posterior zygomatic rootbecomes stronger and more sharply angled,arising laterally from the braincase andforming a triangular shelf that overlies theglenoid fossa (fig. 43B, C).

The occipital region elongates caudallyduring skull development in Pteropus. InAMNH 194276, the ventral rim of theforamen magnum lies only slightly caudalto a relatively small jugular foramen, andanterior to the paracondylar processes. Inadults, the ventral rim of the foramenmagnum is displaced caudally so that it liesposterior to the paracondylar processes, thejugular foramen is much larger in its ros-trocaudal dimension, and the margin of theocciput is located farther caudal from thepetrosal. Modifications in the occiput mayaccount for the apparent decrease in thedeflection of the rostrum seen during de-velopment in many megachiropterans. Berg-mans (1989) noted that young specimens ofmany megachiropteran species (e.g., Nano-nycteris veldkampi) show a greater degree ofrostrum deflection than adults. This alsoholds for Pteropus: in most adult Pteropusspecimens, if the alveolar line is projectedcaudally, it intersects the occiput at thesupraoccipital (see above). In younger ani-mals, such as AMNH 194276, the projectedalveolar line intersects the occiput moredorsally, at the occipitointerparietal suture,indicating a more pronounced rostrum de-flection than seen in adults. Changes incranial deflection presumably occur duringdevelopment by addition of bone in thecentral-stem synchondroses, which elongatesthe basicranium and may rotate it dorsallya few degrees.

SEQUENCE OF BONE FUSION

We investigated the sequence of bonefusion in Pteropus using a series of specimensranging from a fetus to old adults. The twoyoungest specimens in our series were a fetus(Pteropus sp.; DUCEC 831) and a newbornpup (Pteropus capistratus; AMNH 194276)with milk teeth but no permanent teetherupted. The remainder of our sample con-sisted of subadult and adult P. lylei, which wearranged into six composite age stages basedon degree of tooth eruption, tooth wear,tooth loss, and fusion of cranial elements.Stage 1 was defined as including subadultswith no tooth wear and M2 not fully erupted(examples included CM 87972, 87973, andAMNH 240005). Stage 2 was defined asincluding individuals with M2 fully eruptedbut with minimal tooth wear throughout thedentition (e.g., AMNH 237598). Stage 3 wasdefined on the basis of tooth wear (all cheektooth cusps showing signs of wear but ridgesand cusps still distinguishable) and degree offusion of selected cranial elements (e.g.,palatal elements partially fused; e.g., AMNH237594, 237595, and 237599). Stage 4 wascharacterized by the same degree of toothwear as in stage 3 (all cheek tooth cuspsshowing signs of wear) but with additionalcranial fusions suggesting more advanced age(e.g., joints of the basicranium and orbitfused; e.g, AMNH 237593). Stage 5 wasrecognized on the basis of advanced toothwear throughout the dentition, with no ridgesor cusps distinguishable on any molar teeth(e.g., AMNH 30217). Stage 6 was defined byadvanced tooth wear and tooth loss (allcheek teeth lost and canines worn to theirroots; e.g., AMNH 217045). On the basis ofthese categories, we examined the sequenceof bone fusion in our Pteropus sample. Agraphic interpretation of this sequence isshown in figures 44–48.

A distinct pattern of fusion of cranialelements emerges from analysis of specimens

rsynchondrosis indicates the stage in which the suture/synchondrosis is lost. Gray cells indicate thebeginning of a fusion process in one stage that will be completed in later stages. Abbreviations: A prenatalstage; B newborn stage; Sut suture; Syn synchondrosis.


r

Fig. 45. Schematic dorsal (A), ventral (B), and lateral (C) views of the skull of Pteropus lylei based onCM 92972, emphasizing sutures and synchondroses. Numbers represent the age stage of subadults (see textand fig. 44) at which a given suture or synchondrosis is lost completely (indicated by black arrowheads) orincompletely (indicated by open arrowheads).

Fig. 46. Schematic dorsal views of the skull of Pteropus lylei based on CM 92972, showing the sequenceof bone fusion. Each skull is representative of one ontogenetic stage from young subadults to old adults.The figure shows the successive loss of sutures from age stage 1 to 6 (see text and figs. 44 and 45A).


representing the eight age categories definedabove. In the fetus, the alisphenoid and thebasisphenoid form a single ossification, butthe frontals are not completely fused to oneanother: the rostral and caudal ends of theinterfrontal suture disappear shortly afterbirth (based on Pteropus hypomelanusAMNH 159082–159085). A rare example ofa pteropodid specimen showing a completeinterfrontal suture is Dobsonia pannietensisAMNH 108486 (fig. 49). Next, in subadultstage 1, the occipital region is consolidated in

a single unit (figs. 45B, C, 48 part 1). This isfollowed in stage 2 by the fusion of the dorsaland caudal components of the braincase(figs. 45A, 46 part 2). Next, in stage 3, thehard palate and pterygoids start to fuseacross the midline (figs. 45B, 48 part 3).Stage 4 includes a major series of fusions thataffect several regions of the skull, namely thecentral stem, the caudal hard palate, and thelateral braincase and orbit (figs. 45B, C, 47,48 part 4). This is followed in stage 5 by thefrontal, jugal, and palate fusing with the

Fig. 47. Schematic lateral views of the skull of Pteropus lylei based on CM 92972, showing thesequence of bone fusion. Each skull is representative of one ontogenetic stage from young subadults to oldadults. The figure shows the successive loss of sutures and synchondroses from age stage 1 to 6 (see textand figs. 44 and 45C).


remainder of their neighboring bones, as wellas disappearance of the conspicuous naso-maxillary suture (figs. 45, 46–48 part 5). Bythis stage, only the maxilla and the petrosalremain unfused to surrounding bones. Next,in stage 6, the three sutures involving each

premaxilla disappear, as well as one part ofthe occipitomastoid suture (figs. 45, 46–48part 6). Specifically, the occipitomastoid jointis fused between the jugular foramen and themastoid exposure, rostrolateral to the para-condylar process. This is the only part of

Fig. 48. Schematic ventral views of the skull of Pteropus lylei based on CM 92972, showing thesequence of bone fusion. Each skull is representative of one ontogenetic stage from young subadults to oldadults. The figure shows the successive loss of sutures and synchondroses from age stage 1 to 6 (see textand figs. 44 and 45B).


a petrosal joint to be fused, at least inexternal view.

Although we do not have an absolute timescale to contrast with, our observationsindicate that bone fusion continues to occurthroughout life in an orderly fashion. Speci-mens exhibiting the degree of tooth wear ofAMNH 30217 and 217045 (stages 5 and 6)are extremely rare in Pteropus; the mosttypical stage of bone fusion in adult P. lylei isrepresented by AMNH 237593 (stage 4), inwhich a number of joints or parts of jointsare still clearly distinguishable (e.g., thoseinvolving the premaxilla, petrosal, lacrimal,pterygoid, jugal, and parietal, and some oftheir neighboring bones).

A functional interpretation can be deducedfrom the sequence of bone fusion, taking intoaccount the types of joints involved (primar-ily plane or squamous sutures, and synchon-droses) as well as the sequence of fusions.The first bone fusion visible in the pup, theinterfrontal, is a plane suture. We also know

from Pteropus livingstonii AMNH 274466and 274467 that the frontals are fused to theethmoid in the young. This frontoethmoidcomplex can be interpreted functionally asa solidly fused centerpiece that connects therostrum and the cranium through widelyoverlapping surfaces—squamous sutures thatwill fuse much later. Because the overlapzone is so wide (see fig. 26), these squamoussutures may presumably be both very re-sistant to stress and resilient to bendingforces (Evans, 1993). In addition, the zygo-matic arches are rooted posteriorly to thebraincase via another widely overlappingsurface (the sutura squamosa), whereas theanterior root is simply a stout process of themaxilla. As a very general and simplified rule,the basic connecting parts that hold the skulltogether tend to fuse early, whereas widesquamous sutures tend to fuse in later stages.One large plane suture that fuses late is theinterpalatine. This seemingly weak line isbuttressed dorsally by the vomer and the

Fig. 49. Dobsonia pannietensis AMNH 108486, dorsal view. Scale 5 1 mm. Abbreviations: ethethmoid; fr frontal; ip interparietal; lac lacrimal; mx maxilla; mxtu maxillary tuberosity; na nasal; paparietal; pof postorbital foramen; pop postorbital process; sc sutura coronalis; sif sutura interfrontalis; sssutura sagittalis.


osseous and cartilaginous nasal septum, andlaterally by the maxillary tuberosity, whichhas a medial fixation (sensu Cobb, 1943).

COMPARISONS

SKULL SHAPE IN ADULT MEGACHIROPTERANS

Three major structural aspects of skullmorphology vary across megachiropteranspecies: the relative length of the rostrum(producing a continuum from short-faced tolong-faced morphologies), the relative orien-tation of the two fundamental cranial axes,rostral and basicranial (deflection of therostrum), and the development of structuresassociated with the strength of mastication

(e.g., size and orientation of the coronoidprocess and configuration of the temporallines on the skull). These features werediscussed by Andersen (1912) and continueto play a role in modern systematic treat-ments.

Pteropus is a long-faced genus in thecontext of Pteropodidae as a whole. In P.lylei, palatal length accounts for approxi-mately 50% of the length of the skull (figs. 1–3). Andersen (1912) calculated the rostrumlength/skull length ratios for a number ofspecies and divided them into discrete cate-gories for the purpose of composing a key.Springer et al. (1995) and Romagnoli andSpringer (2000) used these data in theirphylogenetic analyses, recognizing three

Fig. 50. Rostral proportions in Pteropodidae, based on 70 species representing all the currentlyrecognized genera. The horizontal axis is the ratio of rostrum length, measured between the rostral ends ofthe nasals and orbit (at the lacrimal), to skull length, measured from the rostral end of the nasals to thecaudalmost portion of the supraoccipital. In Pteropodidae, this index (3 100) varies between 25 (rostrumshortest, roughly J the total length of the skull) and 50 (rostrum longest, roughly K the total length of theskull). A horizontal line represents the observed range for a selected megachiropteran group (tribes andsubfamilies; after Bergmans, 1997). The marks in the axis represent the observed ratios of all speciesmeasured. The mark in Pteropodini represents the position of Pteropus lylei. Note that the Epomophorinispan the entire range observed in Pteropodidae.


character states: state 0 for rostrum ‘‘short,J to 1

5 of skull’’, state 1 for rostrum‘‘medium, M to 2

7 of skull’’, and state 2 forrostrum ‘‘long, 2

5 to K of skull’’. Wemeasured a sample of 70 species from allcurrently recognized megachiropteran generaand found a virtually continuous distributionfor the rostrum/skull length ratio, with nogaps allowing for splitting these data intodiscrete, nonoverlapping character states(fig. 50). As observed by Andersen (1912),epomophorines occupy the entire range ofratios, including genera with the shortest(Casinycteris) and the longest (Hypsignathus)rostra. Macroglossines sensu Andersen(1912; i.e., the six genera of nectar-feedingmegachiropterans), pteropodines, and rou-settines tend to exhibit longer-than-averagerostra, whereas cynopterines, nyctimenines,and dobsonines have shorter-than-averagerostra. Myonycterines sensu stricto (Myonyc-teris + Lissonycteris) occupy an intermediateposition on this continuum. As clearly shownin P. lylei (see above), the length of therostrum tends to increase ontogenetically.

Like rostral length, deflection of therostrum also changes during ontogeny, andthe state of this character may be affected byputative neoteny (e.g., in Nanonycteris; Berg-mans, 1989). However, our examinations ofseries of individuals suggest that adultstypically reach a characteristic degree ofrostral deflection that is consistent acrossspecimens of a given species. As discussed,the degree of rostral deflection can be definedwith reference to the basicranial axis; if thelatter is held horizontal, the alveolar line,representing the facial axis, may cross theocciput at different points: specifically, eitherbelow the basioccipital, at the foramenmagnum, at the supraoccipital, or at theinterparietal (character states used by Gian-nini and Simmons, 2005). Pteropodine mega-bats exhibit two of these conditions: a mod-erate-to-low rostrum deflection (alveolar lineintersects the occiput at the foramen mag-num; seen, for instance, in Pteropus tonganusand P. dasymallus, as well as in two species ofAcerodon) and a moderate-to-high rostrumdeflection (alveolar line intersects the occi-put at the supraoccipital; seen, for instance,in Pteropus admiralitatum, P. giganteus, P.hypomelanus, and P. scapulatus, as well as

in Eidolon, Neopteryx, Pteralopex, and Sty-loctenium). As in its close relative Pteropusgiganteus, in P. lylei the alveolar linecrosses the occiput at the level of thesupraoccipital.

As discussed at length by Andersen (1912),there seems to exist a structural correlationamong several traits related to mastication inPteropus and related genera (probably in allPteropodidae). Briefly, the size and verticalorientation of the coronoid process appearsrelated to the configuration of the temporallines on the skull. These traits, in turn,correlate to the strength of the dentition.Andersen (1912) identified two extremes ofa likely continuous variation. Species char-acterized by an almost vertical and very widecoronoid process, and strongly marked tem-poral lines that join immediately caudal tothe orbits (sometimes forming a sagittalcrest), are also characterized by strongdentition (i.e., elements of large size, some-times with additional cuspidation). An ex-ample is Pteropus anetianus, which alsoexhibits the short rostrum typical of formswith ‘‘heavy’’ dentition (sensu Andersen,1912). At the other end of the spectrum,Andersen (1912) identified species with ex-cessively weak dentition, a trait accompaniedby a sloping (dorsocaudally oriented) andthin coronoid process and weak temporallines that never join behind the orbits or forma sagittal crest. Pteropus scapulatus is anexample of this type; these forms tend to bepollinators (Andersen, 1912). P. lylei belongsto an intermediate category, the hypomelanustype of Andersen (1912), which is character-ized by an intermediate condition in theexpression and development of the dentition,coronoid, and associated traits of the masti-catory apparatus.

INTERSPECIFIC SUTURE VARIATION

Several of the suturae capitis listed in theNAV are absent in the Pteropus examined.The vomeroincisive suture (sutura vomeroin-cisiva) is missing as a consequence of the lackof ossification of the palatine process of thepremaxilla, to which the incisive incisure ofthe vomer articulates in most mammals,including yangochiropteran bats. The eth-moidonasal suture (sutura ethmoidonasalis) is


missing because the frontal has taken overthe whole caudal contact area of the nasal,precluding a nasal-ethmoid contact. Thereduction of the jugal bone—a possiblesynapomorphy of bats (Wible and Novacek,1988; Simmons, 1994)—accounts for the lackof a lacrimozygomatic suture (sutura lacri-mozygomatica). In bats, the jugal is a smallelement in the middle of the zygomatic arch,so the anterior root of the zygoma is entirelywithin the maxilla. Therefore, the lacrimal isisolated from contact with the jugal by thezygomatic process of the maxilla. As in thedog, and most placental mammals, the nasaldoes not contact the lacrimal, the two bonesbeing, in Pteropus, separated by the widefrontomaxillary contact, so the nasolacrimalsuture (sutura nasolacrimalis) is absent. Thefrontal and the squamosal are widely sepa-rated by the parietal and orbitosphenoid, sothe squamosofrontal suture (sutura squamo-sofrontalis) is absent. Finally, the spheno-maxillary suture (sutura sphenomaxillaris) isalso absent.

The frontozygomatic suture (sutura fron-tozygomatica) is present in some megachir-opterans, specifically those species of Acer-odon, Pteralopex, and Pteropus that possessa complete orbital ring produced by ossifica-tion of the orbital ligament. The postorbitalprocess of the frontal contacts the zygomaticarch in these taxa, but the contact occursbetween the frontal and the zygomatic pro-cess of the maxilla, not the jugal, which isgreatly reduced in all bats (Wible andNovacek, 1988; Simmons, 1994).

Some sutures have systematic importance(Andersen, 1912). Such is the case of thethree sutures involving the megachiropteranpremaxilla. First, the nature of the interinci-sive suture varies widely among megachir-opterans. The left and right premaxillae maybe separated and not contact one another(e.g., Boneia), or they may be sutured (e.g.,Rousettus) or fused (e.g., Nyctimene). Simi-larly, the maxilloincisive suture may besutured (the most common condition inmegachiropterans) or fused (e.g., Pteralopex,Styloctenium, Neopteryx). The shape of thepathway of the suture may also vary. Somepteropodines exhibit a ‘‘squared off’’ max-illoincisive suture, whereas in most megabatsthis suture is gently curved. The nasoincisive

suture varies in relative length within Mega-chiroptera. It is a long suture in many of thenectar-feeding bats (e.g., Macroglossus, Mel-onycteris, Notopteris) and exhibits relativereduction in other taxa: it is of moderatelength in most megachiropterans, it is re-duced to a point nasal-premaxilla contactin some others (e.g., many cynopterinesand dobsonines), and the nasal-premaxillacontact is lost in a few forms (e.g., nyctime-nines).

INTERNAL SURFACES OF THE SKULL

Descriptions of the internal surfaces of theskull are almost entirely lacking for bats andare infrequent for mammals in general. Oneexception is the cribriform plate, describedand figured for representatives of most batfamilies by Bhatnagar and Kallen (1974). Thecribriform plate of Pteropus livingstonii (thisstudy) is very similar to that of Pteropusgiganteus, Rousettus leschenaulti, and Cynop-terus sphinx (Bhatnagar and Kallen, 1974),although the cribiform plate of the lattertaxon is relatively wider. These four mega-chiropterans differ from all microchiropter-ans examined by Bhatnagar and Kallen(1974) in that the entire cribriform plate isperforated by cribriform foramina, whereasmicrochiropterans exhibit a cribriform platewith wide nonperforate areas.

For other structures, we compared ourobservations of internal surfaces in Pteropuslivingstonii with the descriptions available forthe dog (Evans, 1993). Pteropus showsa number of striking differences, detailed asfollows.

The nasal bone of Pteropus lacks a nasoeth-moidal crest and fossa. This appears to berelated to the fact that the nasal does notcontact the ethmoid as it does in the dog. Thefrontal process of the nasal overlies only therostral surfaces of the frontal bone in Pteropus.

As discussed above when dealing with theexternal surfaces, the premaxilla lacks a cau-dal projection of the nasal process, and thepalatine processes are missing altogether.These structural differences from the dogalso are reflected on the internal surface ofthe premaxilla. Regarding the maxillaryinternal surface, the most significant differ-ence with respect to the dog is the relative


simplicity of the ventral nasal concha, whichin Pteropus lacks the rich covering of delicatebony scrolls present in the dog. In thepalatine, the chief differences from the dogare the limited dorsal extension of theperpendicular lamina in Pteropus and thenoticeable caudal extension of the horizontallamina, forming a long postdental palateinclusive of the minor palatine foramen (anotch in the dog).

The internal surfaces of the frontoethmoi-dal complex include the frontal, cribriformplate of the ethmoid, ethmoturbinal, andvomer. Differences between Pteropus and thedog include the following. First, the innertable of the frontal (facies interna) is notaffected by the frontal sinus, as the sinus inPteropus is located more rostrally in theinterorbital area. Note, however, that inother megachiropterans, chiefly in cynopter-ines, nyctimenines, and dobsoniines, thefrontal sinus reaches the postorbital area, asin the dog. The inner table of the frontal alsois shaped differently in Pteropus; it does notshow the strong, wedge-shaped internalfrontal crest between the ethmoidal fossaedorsally. Second, the remarkable dorsalextension of the orbitosphenoid in Pteropusleaves a wide notch on the lateral side of thefrontal, thus neatly separating the postorbitalpart of the squama frontalis from the parsorbitalis. Third, ventrally, the ala vomeris isextremely narrow in Pteropus, so the floor ofthe nasal capsule chiefly is exposed ventrally.In the dog, the ala vomeris is significantlywider.

The presphenoid and orbitosphenoids ofPteropus differ notably from those of thedog. Considering the body first, in Pteropusa differentiated rostrum (rostrum sphenoidaleof the dog) is absent; the optic canals aremore rostral in position, so the corpus iselongated caudally; and the sphenoidal si-nuses are very small. The alae in Pteropuspossess a very large vertical component thatcontributes significantly to the orbit wall,reaching two-thirds of the orbit height, anarrangement that stands in striking contrastto the limited orbital exposure of the orbito-sphenoid in the dog. The main difference canbe thought of as a combination of twomodifications: an enlargement of the alaeand a rostral displacement of the yoke.

The basisphenoid and alisphenoid ofPteropus also differ significantly from thoseof the dog, especially in dorsal view. InPteropus, there is no trace of alar canal andhence no differentiated foramen rotundum,its contents instead being transmitted directlyto the sphenorbital fissure. The sella turcica isalso different in being significantly elongatedand in lacking a distinct caudal clinoidprocess (processus clinoideus caudalis) anddorsum sellae. The sizable pterygoid pro-cesses present in the dog are minute inPteropus. Caudally, Pteropus exhibits a verydistinct epitympanic wing of the alisphenoid,which is absent or inconspicuous in the dog.

The internal surface of the parietal com-plex in Pteropus differs from that of the dogin several important aspects. First, Pteropuswholly lacks the tentorial process (processustentoricus). Second, due to the fact that in thedog the vascular supply to the m. temporalisis entirely extracranial, all structures (sulciand foramina) directly associated with theintracranial course of the ramus superior andrami temporales in Pteropus are correspond-ingly absent in the dog. Third, the develop-ment and conspicuousness of the sulcus forthe transverse sinus is much less marked inPteropus. Fourth, the interparietal in the dogis a wedge-shaped bone fitting a narrowinterparietal space and is more intimatelyassociated with the supraoccipital than withthe parietals. The interparietal in Pteropus isa subcircular, domed plate more intimatelyassociated with the parietal than with thesupraoccipital. Additionally, the interparietalof Pteropus lacks a foramen for the dorsalsagittal sinus (foramen sinus sagittalis dorsa-lis). Finally, the degree of parietal overlap ofthe frontal is much more pronounced inPteropus than in the dog, and the parietaloverlaps the supraoccipital.

Comparisons between the internal surfaceof the squamosal in Pteropus and the dog aredifficult because in the dog the squamosal issolidly integrated in the temporal complex.One difference that should be noted, howev-er, is the absence in the dog of the sulcus thatleads the ramus superior outside the brain-case through the foramina for the ramitemporales. This sulcus is absent becausethe ramus superior and the rami temporalesare entirely lacking in the dog. Also, in


Pteropus, the transverse sulcus is less marked,and even less so in the parietal with respect tothe squamosal (see above).

Major differences exist between Pteropusand the dog in the internal surfaces of theoccipital complex. These include the absencein Pteropus of an occipital contribution to thesulcus for the venous transverse sinus (alsoreduced in the parietal) and the absence ofthe condyloid canal (canalis condylaris).Another difference occurs in the shape ofthe foramen magnum, which is rhomboidalin Pteropus but is dorsally constricted in thedog by the presence of the paired nuchaltubercles (tuberculum nuchale) in most adultindividuals.

FORAMINA

Species of Pteropus including P. lylei showneither the full set of foramina present inMegachiroptera as a group, nor the samedegree of development in all the foraminawhose presence is shared with other forms.Here we point out the differences andgeneralities that arise from comparing P.lylei with other Pteropus species, as well aswith other pteropodine and nonpteropodinemegachiropterans.

BASICOCHLEAR FISSURE, PIRIFORM FE-

NESTRA, AND JUGULAR FORAMEN: Ptero-pus lylei lacks an alicochlear commissureand has a robust basicochlear commissure.As a consequence, the basicochlear fissureis connected to the piriform fenestrarostrolaterally, and is widely separatedfrom the jugular foramen caudally. Threemodifications with respect to this patternin other pteropodids are worth mentioning.First, the alicochlear commissure may bepresent, so the piriform fenestra is wellseparated from the basicochlear fissure(e.g., in Nyctimene). Second, the basico-chlear commissure may be greatly reduced,so both the basicochlear fissure and thejugular foramen are enlarged (e.g., inCynopterus). Third, in species of Pteralo-pex and large Pteropus and Acerodon, thebasicochlear fissure may be concealed inventral view by a comparatively strongmuscular tubercle (tuberculum musculare)of the basioccipital (not developed in P.lylei) and a similarly enlarged medial ridge

on the promontorium (present in adult P.lylei).

FORAMEN OVALE: Pteropus lylei exhi-bits a large opening in the alisphenoid thatcorresponds to the foramen ovale + thecaudal alar foramen of the dog. Confluenceof these foramina is observed in manyPteropus species (including P. livingstoniiand P. temminckii), but the two openingsare separated in other species (e.g., P.admiralitatum, P. tonganus) and still othertaxa show varying degrees of separation indifferent individuals (e.g., P. hypomelanus, P.giganteus). When not fully separated, theforamina are found in a distinct elongate,shallow pit. Other pteropodines (exceptNeopteryx) show two well-separated open-ings. The foramen ovale and caudal alarforamen are similarly separate in Rousettus,Eonycteris, Boneia, Stenonycteris, Eidolon,Lissonycteris, Myonycteris, Aproteles, Dobso-nia, most epomophorines (except Epomo-phorus gambianus and Nanonycteris), somecynopterines (Balionycteris, Chironax,Sphaerias, Pentethor, Thoopterus, and Alio-nycteris), and one macroglossine (Melon-ycteris woodfordi). In contrast, these foram-ina are confluent in the remainder ofcynopterines (Cynopterus, Megaerops, Pteno-chirus, Aethalops, Dyacopterus, and Haplo-nycteris), macroglossines, and nyctimenines(Nyctimene and Paranyctimene).

FORAMEN IN THE POSTPALATINE TO-

RUS: In all species of Pteropus, the foramenin the postpalatine torus is absent. Incontrast, such a foramen is present in manyother genera, including Rousettus and Eido-lon. Based on Monodelphis (Wible, 2003), theforamen in the postpalatine torus likelytransmits contents from the minor palatineforamina to the soft palate (Wible, 2003).

FORAMEN FOR THE RAMUS SUPRAORBI-

TALIS: Pteropus lacks a foramen for theramus supraorbitalis of the ramus superior inthe sphenoparietal suture (the cranio-orbitalforamen of Wible, 1987, or the anterioropening of the orbitotemporal canal of Wibleand Gaudin, 2004). This foramen is presentin many other megachiropterans, irrespectiveof skull size (e.g., in the large Eidolon and thesmall Otopteropus). In many of these taxa(e.g., in Rousettus), the orbitotemporal canalis externally visible. The intracranial course


of the ramus supraorbitalis of the ramussuperior extends from the foramen in thesphenoparietal suture to a rather ill-definedarea in the suprameatal bridge. As pointedout above, in Pteropus (e.g., in specimens ofour sample of P. livingstonii) the orbitotem-poral canal can be observed in the medialsurface of the parietal in disarticulated skulls.

FORAMINA FOR RAMI TEMPORALES:Whereas Pteropus presents the typical multi-ple openings per side of the foramina for therami temporales in the sutura squamosa,some megachiropterans have lost these fo-ramina entirely. This is the case in allepomophorines except Casinycteris and Sco-tonycteris, some cynopterines (e.g., Chironaxand Otopteropus), and all macroglossinessensu Andersen (1912). This loss implies thatthe vascular supply for the m. temporalisfrom the stapedial artery system is absent,probably having been replaced by an extra-cranial supply from the external carotidsystem, as in the dog.

INFRAORBITAL FORAMEN: Most mega-chiropterans, including species of Pteropus,exhibit a short infraorbital canal that opensvery close to the orbital rim. Two genera,Notopteris and Melonycteris (forming theNotopteris section of Andersen, 1912), havean infraorbital foramen located more anteri-orly, at a greater relative distance from theorbital rim. As a consequence, the infraorbi-tal canal has a longer intramaxillary course.

LACRIMAL FORAMEN: In Pteropus, thelacrimal foramen is large and conspicuous,representing the typical condition in mega-chiropterans. By contrast, in Nyctimene thelacrimal foramen is comparatively very small,as in many microchiropterans, in which thelacrimal foramen is greatly reduced orabsent.

MAJOR PALATINE FORAMEN: In Ptero-pus lylei and several other species of Pteropus,the major palatine foramen is located in thetransverse palatine suture roughly at the levelof the P4–M1 embrasure. In other species ofPteropus (e.g., P. scapulatus), the foramen islocated more rostrally, at the level of P4. Thiscondition is also seen in other pteropodinesand Eidolon. The major palatine foramen iseven more rostrally located in certain speciesof Pteralopex (e.g., P. atrata and P. anceps),in which the major palatine foramen is

located at the level of P3, lying entirelywithin the palatine process of the maxilla. Bycontrast, many epomophorines and cynop-terines have the major palatine foramensituated caudal to the level of M1, in whichcase the foramen lies entirely within thehorizontal process of the palatine bone.

MASTOID FORAMEN: In Pteropodidae,this foramen exhibits three different sizes.The species of Pteropus we examined, as wellas some other megachiropterans (e.g., Nycti-mene), show a remarkably small mastoidforamen. By contrast, some epomophorinepteropodids have a very large mastoidforamen (e.g., Hypsignathus, Epomophorus).The remainder of our sample presents anintermediate condition.

MINOR PALATINE FORAMEN: In Ptero-pus lylei, the minor palatine foramen opens inthe substance of the horizontal process of thepalatine. This is also the case in the majorityof megachiropterans. The most significantmodification found in megachiropterans is inthe pteropodine Neopteryx frosti. In thisspecies, a large notch opens on the lateralmargin of the postdental palate in place ofthe foramen. This resembles the conditionseen in the dog, in which the minor palatinenerve and vessels penetrate the ventral side ofthe palate through an unnamed notch in thecaudal part of the maxillary bone. InNeopteryx, however, the notch is entirelywithin the horizontal process of the palatine.Less extraordinary modifications are foundin species of Nyctimene (e.g., N. major) andPteropus (e.g., P. hypomelanus). In theseforms, the postdental palate is constrictedlaterally to produce the ‘‘pandurate’’ (hour-glass-shaped) condition described by Ander-sen (1912) for Nyctimene. In these palates,the minor palatine foramen can be very closeto the lateral margin of the postdental palate,and in some individuals (e.g., P. hypomelanusAMNH 159043) just a tiny splint of boneprevents the foramen from being a notch.

OPTIC CANAL: Limited variation existsregarding the shape of the optic canal. Ina number of species of pteropodines (e.g.,Pteropus niger, Pteropus voeltzkowi, Acero-don jubatus, Pteralopex acrodonta), the opticcanal protrudes rostrodorsolaterally asa short tube, with a distinct depressionformed rostroventral to that tube in the


orbitosphenoid. In all other megachiropter-ans, including P. lylei, the optic canal consistsof only a simple foramen and there is nodevelopment of a tubelike structure.

POSTORBITAL FORAMEN: This foramenis conspicuous and consistently present in allspecies of Pteropus and many other mega-chiropterans. In Dyacopterus, Pteralopex(e.g., Pteralopex atrata BMNH 89.4.3.3),and Harpyionycteris, the postorbital foramenis reduced in size and may be absent on oneor both sides in some individuals. Finally, inDobsonia minor, many cynopterines (all butCynopterus, Megaerops, Ptenochirus, andDyacopterus), and all nyctimenines, the post-orbital foramen is entirely lacking in allindividuals.

SPHENORBITAL FISSURE AND ALAR CA-

NAL: Pteropus is typical among megachir-opterans in that a single opening—thesphenorbital fissure—transmits all of thestructures that pass through the orbitalfissure, foramen rotundum, and alar canal(canalis alaris) of the dog. However, twospecies in the related genus Pteralopex exhibita typical alar canal (based on Pteralopexanceps BMNH 8.11.16.7 and Pteralopexacrodonta BMNH 77.3097). In these taxa,the caudal alar foramen is widely separatedfrom the foramen ovale posteriorly, and therostral alar foramen is separated anteriorlyfrom the sphenorbital fissure by a bonywall of the alisphenoid. In contrast, theother two species of Pteralopex examinedby us (Pteralopex flanneryi USNM 277112,276973-4, and Pteralopex atrata BMNH88.1.5.9, 89.4.3.3, 34.4.2.31, 89.4.3.1) showthe typical megachiropteran condition, asdescribed above. In the dog, the foramenrotundum is clearly differentiated and opensin the dorsal side of the alar canal. It is notpossible to determine whether the foramenrotundum is differentiated or not in intactskulls of P. anceps and P. acrodonta. Otherforamina were not examined in detail ina sufficiently complete sample of megachir-opterans.

SUMMARY: From the available compar-isons, we conclude that Pteropus seemstypical among megachiropterans in the pres-ence and development of most foramina,while showing significant variations in someareas. Some foramina present in most mega-

bats are absent in Pteropus, including theforamen in the postpalatine torus and theanterior opening of the orbitotemporal canal.One foramen (the mastoid foramen) is re-duced in relative size in Pteropus in compar-ison to the condition seen in other megabats.Still other foramina have been modified bycoalescence: foramen ovale + caudal alarforamen (in some species like P. lylei), andthe piriform fenestra + basicochlear fissure +carotid foramen. In addition, Pteropus andmegachiropterans as a group exhibit thefollowing noteworthy conditions: an incisivefissure instead of paired incisive foramina,resulting from the lack of ossification of thepalatine process of the premaxilla; a sphenor-bital fissure that includes the contents of theorbital fissure, rostral alar canal, and fora-men rotundum; a well-defined postorbitalforamen carrying an apparently uniqueartery; a shortened infraorbital canal withthe correspondingly retracted position of theinfraorbital foramen (except Macroglossus,Melonycteris, and Notopteris); a minor pala-tine foramen in the substance of the post-dental palate (horizontal process of thepalatine); and lack of the posttemporalforamen.

DENTITION

The most complete dental formula knownin bats is I2/3, C1/1, P3/3, M3/3 3 2 5 38,which is seen in echolocating bats such asMyotis. Megachiropterans have reduced den-tal formulae, the most complete (I2/2, C1/1,P3/3, M2/3 3 2 5 34) being present as a rulein Pteropus but also in other genera such asRousettus and Eidolon. P. lylei is no excep-tion, and the morphology of its dentition isalso typical of both the genus and thehypomelanus type. Significant variations indental formulae and tooth morphology existamong megachiropterans, most of whichwere discussed in detail by Andersen (1912).Seven genera and many species were discov-ered after the publication of Andersen’smonographic treatment, but no particularlydifferent tooth morphologies occur in thegenera described after 1912. We direct thereader to Andersen (1912) for a completeanalysis of dental variation in Megachirop-tera. Important additional discussion is


found in Hill and Beckon (1978), and in theremarkable series of papers by Win Berg-mans (Bergmans, 1976, 1977, 1980, 1988,1989, 1990, 1994, 1997, 2001; Bergmans andRozendaal, 1988).

The homology of specific dental structures(such as cusps, basins, and ridges) withrespect to a typical tribosphenic molar isuncertain. Miller (1907), on the basis ofcomparisons with frugivorous phyllostomidmicrochiropterans, assumed that the mega-chiropteran upper premolars and molarseach bear a protocone (medial cusp andridge) and a paracone (lateral cusp andridge), whereas the lower molars bear a me-taconid (medial cusp and ridge) and a proto-conid (lateral cusp and ridge). Andersen(1912) arrived at a similar conclusion basedon comparisons with Talpa europaea, a molewith dilambdodont molars. Andersen (1912)postulated that the lateral ridge of the uppermolars of megabats corresponded to a para-cone + metacone, and the medial ridgecorresponded to the protocone + hypocone;in the lower molars, the lateral ridge corre-sponded to a protoconid + hypoconid, andthe medial ridge to paraconid + metaconid +entoconid. Both Miller (1907) and Andersen(1912) agreed that megachiropterans lacka stylar shelf; that is, the lateralmost cuspsof a chiropteran tribosphenic molar (para-style, mesostyle, and metastyle) are entirelyabsent.

Although most megachiropterans havesimplified cheek teeth characterized by medi-al and lateral ridges, several taxa exhibitmulticuspidate cheek teeth, most notablyHarpyionycteris and Pteralopex. Miller(1907) and Andersen (1912) believed thatadditional cusps were the product of second-ary divisions of the basic megachiropteranlateral and medial ridges. However, otherauthors, including Slaughter (1970; see alsoThenius, 1989) homologized all individualcusps with normal tribosphenic elements,stating that an upper molar of Harpyionyc-teris exhibits a paracone, protocone, meta-cone, hypocone, and metastyle, and that thelower molar supports a protoconid, metaco-nid, hypoconid, entoconid, and two stylids(the proto- and metastylid). Peterson andFenton (1970) dismissed the cusp homologiesof Slaughter (1970) on the basis of inconsis-

tent variation they observed in series ofspecimens of Harpyionycteris. In turn, Hilland Beckon (1978), on the basis of anextensive comparative study of the dentitionin Pteralopex, favored Andersen’s (1912)view that the multicuspidate condition ofPteralopex was probably derived from moretypical pteropodine molars, such as those ofthe pselaphon species group within Pteropus.We concur with Hill and Beckon (1978) inconcluding that support for detailed homol-ogy statements linking multiple cusps ofmolariform teeth in megachiropterans likePteralopex with the cusps of the microchir-opteran dentition is lacking or contradictory.While the loss of the stylar shelf seemsa safe assumption, there is little or nosupport for identification of megachirop-teran cusps with typical tribosphenic ele-ments. Certainly, the most conservativeapproach to this unresolved problem wouldbe to recognize that the two main ridgesand accompanying cusps of the megachir-opteran cheek tooth may derive from non-stylar, large tribosphenic cusps, but thespecific homology of contributing cuspsremains unknown.

DIRECTIONS FOR FUTURE RESEARCH

In this work, we provide a detailed de-scription of external and internal surfaces ofthe skull of Pteropus, a study of the dentitionand foramina contents, and propose a stan-dard nomenclature for bat skull structures.We also provide a series of comparisons thataddress homology of structures, cranialontogeny, and the level of generality of ourfindings within Pteropodidae as a whole. Thenext obvious step would be to providecomparisons with other bats, but suchanalyses are far beyond the scope of thecurrent study. Echolocating bats, represent-ing either a single clade Microchiroptera(Simmons, 1998; Simmons and Geisler,1998, 2002) or two lineages (with yinochir-opteran bats forming a clade with megachir-opterans; Teeling et al., 2000, 2005), areenormously diverse in terms of skull mor-phology (for images of skulls of most batgenera, see Koopman, 1994). Indeed, it islargely on the basis of craniodental variationthat 18 families of echolocating bats are now


recognized (Simmons, 1998, 2005). It is ourintention to follow the current contributionwith a similar study of skull morphology inmicrobats, including detailed considerationsof the cranial modifications associated withevolution of echolocation.

Another area that has received inadequateattention is the morphology of the post-cranial skeleton of bats. At least one broadsurvey of skeletal variation has been pub-lished (Walton and Walton, 1970), as well asfocused studies of limb girdles (e.g., Waltonand Walton, 1968; Strickler, 1978), but notruly comprehensive description has beencompleted that addresses anatomical nomen-clature of all postcranial structures. Someskeletal features have been given differentnames by different authors, whereas otherstructures remain unnamed, and homologyof some structures has yet to be fully resolved(e.g., see character descriptions in Simmonsand Geisler, 1998). As with the skull, we hopeto provide a solid basis of description andnomenclature for future comparative func-tional analyses, systematic studies, and phy-logenetic analyses involving bat postcranialmorphology.

ACKNOWLEDGMENTS

We are thankful to Patricia Wynne andGina Scanlon for the illustrations. PaulaJenkins (Natural History Museum, London),Mark Engstrom and Burton Lim (RoyalOntario Museum), and Bruce Patterson andLarry Heaney (Field Museum, Chicago)permitted access to specimens in their care.Mariko Kageyama kindly assisted with pho-tography, and Roberto Keller and AngelaKlaus assisted with SEM images. We offerspecial thanks to Ana C. Quinteros Orio.Funding for this report was provided by theNational Science Foundation (grant DEB-0129127 to JRW and grant DEB-9873663 toNBS) and Coleman and Vernay postdoctoralfellowships at the AMNH to NPG.

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APPENDIX 1

LIST OF ANATOMICAL TERMS

Terms used in the text are listed alphabet-ically, along with references and/or NominaAnatomica Veterinaria (NAV) and NominaEmbryologica Veterinaria (NEV) equiva-lents. Single asterisks (*) indicate structuresdiscussed in the text but absent in Pteropuslylei (e.g., Alar canal). Double asterisks (**)indicate structures discussed in the text whosedevelopment in P. lylei is minimal ornegligible, or structures of uncertain homol-ogy (e.g., Dorsum sellae).

Abducens nerve (5 cranial nerve VI)—Nervus abducens (NAV)

Accessory nerve (5 cranial nerve XI)—Nervus accessorius (NAV)

Accessory palatine artery (Evans, 1993)

Accessory palatine foramen (Wible andRougier, 2000) 5 Minor palatine foramen(Evans, 1993)

Accessory palatine nerve—Nervus palatinusaccessorius (NAV)

Ala hypochiasmatica (De Beer, 1937)

Alae of vomer—Alae vomeris (NAV)

Ala orbitalis (5 orbitosphenoid) (NAV)

Ala temporalis (5 alisphenoid) (NAV)

Alar canal (5 alisphenoid canal)*—Canalisalaris (NAV)

Alicochlear commissure* (De Beer, 1937)—Processus cochlearis ossis sphenoidalis(Henson, 1970)

Alisphenoid—Os basisphenoidale, ala tem-poralis (NAV)

Alveolar canal—Canalis alveolaris (NAV)

Alveolar foramina—Foramina alveolaria(NAV)

Alveolar line or border—Margo alveolaris(NAV)

Alveolar nerve—Nervus alveolaris (NAV)

Alveolar process or surface of maxilla—Processus alveolaris (NAV)

Alveoli—Alveoli dentales (NAV)

Ampulla—Ampulla ossea (NAV)

Anastomotic artery 5 Arteria anastomotica(Wible, 1987)

Angle of mandible—Mandibula, angulusmandibulae (NAV)

Angular process**—Processus angularis(NAV)

Anterior basicochlear commissure* (De Beer,1937)

Anterior cornu (5 hyoid arch) (Sprague,1943)—Cornu minus (NAV)

Anterior crus (5 leg) of ectotympanic—Annulus tympani, crus anterior (NAV)

Anterior (5 rostral) crus (5 leg) of stapes—Stapes, crus rostrale (NAV)

Anterior division of ramus superior (Wible,1987)

Anterior mental foramen: see Mental fora-men

Anterior opening, orbitotemporal canal*(Rougier et al., 1992) 5 Cranio-orbitalforamen (5 foramen for ramus supraorbi-talis) (Wible, 1987)

Anterior paraseptal cartilages—Cartilagoparaseptalis anterior (Jurgens, 1963)

Anterior semicircular canal—Canalis semi-circularis anterior (NAV)

Apex of alveolus—Apex radici dentis (NAV)

Apex of skull (Evans, 1993)

Apex partis petrosae (NAV)

Arch of cricoid—Arcus cartilaginis cricoi-deae (NAV)

Arcus alveolaris (NAV)

Area cochleae (NAV)

Area nervus facialis (NAV)

Arteria diploetica magna (Hyrtl, 1853, 1854;Wible, 1987)

Artery of postorbital foramen (this study)

Artery of pterygoid canal (Evans, 1993)

Articular (Goodrich, 1930)

Articulatio temporohyoidea (NAV)

Arytenoid cartilage—Cartilago arytenoidea(NAV)

Atlanto-occipital joint—Articulatio atlanto-occipitalis (NAV)

Auditory capsule—Capsula otica (NEV)

Auditory region—Auris (NAV)

Auditory tube—Tuba auditiva (NAV)

Basicochlear fissure (5 basicapsular fenestra;5 petro-occipital fissure) (De Beer,1937)—Fissura petro-occipitalis (Evans,1993)

Basicranial axis (Andersen, 1912)

Basicranium—Basis cranii interna et externa(NAV)

Basihyoid—Basihyoideum (NAV)

Basihyoid cartilage—Cartilago basihyoidea(NAV)

Basilar artery—Arteria basilaris (NAV)


Basioccipital—Os occipitale, pars basilaris(NAV)

Basioccipital pit (this study)Basipharyngeal canal (Evans, 1993)Basisphenoid—Os basisphenoidale, corpus

(NAV)Body of mandible—Corpus mandibulae

(NAV)Body of maxilla—Os maxillare, corpus max-

illae (NAV)Body of premaxilla—Corpus ossis incisivi

(NAV)Brain—Encephalon (NAV)Braincase—Calvaria (NAV)Buccal (5 vestibular; lateral) surface of

mandible—Mandibula, facies buccalis(NAV)

Canines—Dentes canini (NAV)Capsuloparietal emissary vein (Gelderen,

1924)Carnassial tooth* (Evans, 1993)—Dens sec-

torius (NAV)Carotid foramen (Wible and Gaudin,

2004)—Canalis caroticus (NAV)Carotid sulcus—Sulcus caroticus (NAV)Cartilage ‘‘N’’ (Jurgens, 1963)Caudal alar foramen*—Foramen alare cau-

dale (NAV)Caudal clinoid process*—Os basisphenoida-

lis, processus clinoideus caudalis (NAV)Caudal cornu of thyroid—Cartilago thyroi-

dea, cornu caudale (NAV)Caudal entotympanic—Caudales entotympa-

nicum (Klaauw, 1922)Caudal meningeal artery—Arteria meningea

caudalis (NAV)Caudal nasal nerve—Nervus nasalis caudalis

(NAV)Caudal palatine foramen (Evans, 1993)—

Foramen palatinum caudale (NAV)Caudal process of pterygoid (this study)Caudal thyroid notch—Incisura thyroidea

caudalis (NAV)Caudal tympanic process of petrosal (Mac-

Phee, 1981)Caudolateral angle of parietal (this study)Caudoventral margin of parietal (this study)Cavernous sinus—Sinus cavernosus (NAV)Cavum epiptericum (Gaupp, 1902, 1905; De

Beer, 1937)Cavum supracochleare (5 genu of facial

canal) (Voit, 1909; De Beer, 1937)—Geni-culum canalis facialis (NAV)

Cavum tympani (NAV)Central stem (5 parachordal plate) (De Beer,

1937)Ceratohyoid—Ceratohyoideum (NAV)Ceratohyoid cartilage—Cartilago cerato-

hyoidea (NAV)Cerebellum (NAV)Cerebral juga—Juga cerebralia (Evans, 1993)Choanae (NAV)Chorda tympani nerve—Chorda tympani

(NAV)Cingulum of teeth—Dentes, cingulum

(NAV)Circle of Willis (5 arterial circle of brain)—

Circulus arteriosus cerebri (NAV)Cochlear area of petrosal—Area cochleae

(NAV)Cochlear canaliculus—Apertura externa can-

aliculus cochleae (NAV) 5 Aqueductuscochleae (Evans, 1993)

Cochlear duct—Ductus cochlearis (NAV)Cochlear fossula (MacPhee, 1981)Cochlear nerve—Nervus cochlearis (NAV)Common nasal meatus—Meatus nasi com-

munis (NAV)Conchal crest—Crista conchalis (NAV)Condyloid canal*—Canalis condylaris

(NAV)Condyloid crest of mandible—Mandibula,

crista condyloidea (NAV)Condyloid fossa—Fossa condylaris ventralis

(NAV)Coronal (5 frontoparietal) suture—Sutura

coronalis (NAV) 5 Sutura frontoparietalis(Evans, 1993)

Coronoid crest—Crista coronoidea (Evans,1993)

Coronoid process—Processus coronoideus(NAV)

Cranio-orbital foramen (5 foramen forramus supraorbitalis)* (Wible, 1987)

Cranioventral process of arytenoid (thisstudy)

Cranium (NAV)Crest of vomer—Crista vomeris (NAV)Cribriform foramina—Foramina laminae

cribrosae (NAV)Cribriform plate of ethmoid—Os ethmoidale,

lamina cribrosa (NAV)Cricoarytenoid articulation—Articulation

cricoarytenoidea (NAV)Cricoid cartilage—Cartilago cricoidea

(NAV)


Cricothyroid articulation—Articulatio cri-cothyroidea (NAV)

Crista galli of ethmoid—Os ethmoidale,crista galli (NAV)

Crista parotica of petrosal (De Beer, 1937)

Crista semicircularis (Jurgens, 1963)

Crown of teeth—Dentes, corona dentis(NAV)

Crus breve of incus—Incus, crus breve(NAV)

Crus commune of semicircular canals (Wible,1990)—Crus osseum commune (Henson,1970)

Cusp of teeth—Dentes, cuspis dentis(NAV)

Deciduous teeth—Dentes decidui (NAV)

Deep petrosal nerve—Nervus petrosus pro-fundis (NAV)

Diastema (NAV)

Digastric muscle—Musculus digastricus(NAV)

Digital impressions—Cranium, lamina in-terna, impressiones digitatae (NAV)

Dorsal condyloid fossa—Fossa condylarisdorsalis (Evans, 1993)

Dorsal intraoccipital synchondrosis—Synch-ondrosis intraoccipitalis squamolateralis(NAV)

Dorsal lamina of cricoid—Lamina cartilagi-nis cricoideae (NAV)

Dorsal nasal meatus—Meatus nasi dorsalis(NAV)

Dorsal process of arytenoid (this study)

Dorsal surface of basisphenoid—Os basi-sphenoidalis, facies cerebralis (NAV)

Dorsal surface of palate—Os palatinum,facies nasalis (NAV)

Dorsal vestibular area of petrosal—Areavestibularis superior (NAV)

Dorsum sellae** (NAV)

Ectopterygoid process (Novacek, 1986)

Ectotympanic—Annulus tympanicus (NAV)

Embrasure—Septa interalveolaria (NAV)

Emissary vein of cavernous sinus (Evans,1993)

Encephalic surface of petrosal—Os tempor-ale, pars petrosa, facies encephalica(Evans, 1993)

Endolymphatic duct—Ductus endolymphati-cus (NAV)

Endoturbinates—Endoturbinalia (NAV)

Entoconid (Miller, 1907)

Entotympanic—Entotympanicum (Klaauw,1922) 5 Os temporale, pars endotympa-nica (NAV)

Epiglottic cartilage—Cartilago epiglottica(NAV)

Epihyoid—Epihyoideum (NAV)Epihyoid cartilage—Cartilago epihyoidea

(NAV)Epiphyseal cartilage—Cartilago epiphysialis

(NAV)Epitympanic angle of parietal (this study)Epitympanic margin of parietal (this study)Epitympanic recess—Recessus epitympani-

cus (NAV)Epitympanic wing of alisphenoid (MacPhee,

1981)Epitympanic wing of parietal (this study)Ethmoid—Os ethmoidale (NAV)Ethmoidal artery—Arteria ethmoidalis

(NAV)Ethmoidal crest of palatine—Crista ethmoi-

dalis (NAV)Ethmoidal foramen/notch—Foramen eth-

moidale (NAV)Ethmoidal fossae—Fossae ethmoidales

(NAV)Ethmoidal nerve—Nervus ethmoidalis

(NAV)Ethmoidomaxillary suture—Sutura ethmoi-

damaxillaris (NAV)Ethmoidonasal suture*—Sutura ethmoido-

nasalis (NAV)Ethmoturbinal—Ethmoturbinale (NAV)Exoccipital—Os occipitale, pars lateralis

(NAV)External acoustic meatus—Meatus acusticus

externus (NAV)External acoustic porus—Porus acusticus

externus (NAV)External carotid artery—Arteria carotis ex-

terna (NAV)External nasal aperture—Apertura nasi ossea

(NAV)External occipital protuberance—Protuber-

antia occipitalis externa (NAV)External occipital crest—Crista occipitalis

externa (NAV)External ophthalmic (5 orbital) artery (5

ramus orbitalis)—Arteria ophthalmica ex-terna (NAV)

External surface of parietal—Os parietale,facies externa (NAV)

Eyeball—Bulbus oculi (NAV)


Eyelids—Palpebrae (NAV)Facial canal—Canalis facialis (NAV)Facial nerve (5 cranial nerve VII)—Nervus

facialis (NAV)Facial nerve area—Area nervus facialis

(NAV)Facial sulcus (MacPhee, 1981)Facial surface of lacrimal—Os lacrimale,

facies facialis (NAV)Fenestra cochleae (NAV)Fenestra vestibuli (NAV)Fifth pharyngeal arch—Arcus pharyngeus

quintus (NEV)Footplate (5 base) of stapes—Stapes, basis

stapedis (NAV)Foramen acusticum inferius 5 Ventral ves-

tibular area (Evans, 1993)Foramen acusticum superius 5 Facial canal

+ dorsal vestibular area (Evans, 1993)Foramen alare parvum* (NAV)Foramen for chorda tympani nerve (Jurgens,

1963)Foramen for dorsal sagittal sinus*—Fora-

men sinus sagittalis dorsalis (NAV)Foramina for frontal diploic vein (Thewissen,

1989)Foramen for ramus temporalis (5 subsqua-

mosal foramen) (Wible and Gaudin, 2004;Wible et al., 2004)

Foramen in the postpalatine torus* (Wible,2003)

Foramen for zygomatic nerve* (Evans, 1993)Foramen magnum (NAV)Foramen ovale (NAV)Foramen rotundum* (NAV)Foramen singulare* (NAV)Foramen spinosum* (NAV)Forehead—Frons (NAV)Fossa cerebellaris of petrosal—Fossa cere-

bellaris, pars petrosa (NAV)Fossa for lacrimal sac—Fossa sacci lacrima-

lis (NAV)Fossa for stapedius muscle (MacPhee,

1981)—Fossa m. stapedius (Evans, 1993)Fossa for tensor tympani muscle (MacPhee,

1981)—Fossa m. tensor tympani (Evans,1993)

Fossa incudis (MacPhee, 1981)Fossa infratemporalis (NAV)Fossa temporalis (NAV)Fourth pharyngeal arch—Arcus pharyngeus

quartus (NEV)Frontal—Os frontale (NAV)

Frontal angle of parietal—Os parietale,angulus frontalis (NAV)

Frontal crest—Os frontale, facies interna,crista frontalis (NAV)

Frontal diploic vein—Vena diploica frontalis(NAV)

Frontal margin of parietal—Os parietale,margo frontalis (NAV)

Frontal nerve—Nervus frontalis (NAV)

Frontal process of jugal—Os zygomaticum,processus frontalis (NAV)

Frontal process of maxilla—Os maxillare,processus frontalis (NAV)

Frontal process of nasal—Os nasale, proces-sus frontalis (NAV)

Frontal region—Regio frontalis (NAV)

Frontal sinus—Sinus frontalis (NAV)

Frontoethmoidal suture—Sutura frontoeth-moidalis (NAV)

Frontolacrimal suture—Sutura frontolacri-malis (NAV)

Frontomaxillary suture—Sutura frontomax-illaris (NAV)

Frontonasal suture—Sutura frontonasalis(NAV)

Frontopalatine suture—Sutura frontopala-tina (NAV)

Frontozygomatic suture*—Sutura frontozy-gomatica (NAV)

Geniculate ganglion—Ganglion geniculi(NAV)

Gonial (5 prearticular) (Gaupp, 1908; DeBeer, 1937)

Glaserian fissure—Fissura Glaseri (Klaauw,1931) 5 Fissura petrotympanica (NAV)

Glenoid fossa (5 retroarticular fossa)—Fossa mandibularis (NAV)

Glossopharyngeal nerve (5 cranial nerveIX)—Nervus glossopharyngeus (NAV)

Greater petrosal nerve—Nervus petrosusmajor (NAV)

Groove for middle meningeal artery—Sulcusarteriae meningeae mediae (Evans, 1993)

Gyri of brain—Cerebrum, gyri cerebri(NAV)

Hamulus—Hamulus pterygoideus (NAV)

Hard palate—Palatum osseum (NAV)

Head of malleus—Caput mallei (NAV)

Head of stapes—Caput stapedis (NAV)

Hiatus Fallopii (McDowell, 1958) 5 Petrosalcanal (Evans, 1993)

Horizontal part of vomer (Evans, 1993)


Horizontal process of palatine—Os palati-num, lamina horizontalis (NAV)

Hyoid apparatus—Apparatus hyoideus(NAV)

Hypocone** (Miller, 1907)Hypoconid** (Miller, 1907)Hypoglossal canal* (Evans, 1993)Hypoglossal foramen—Canalis n. hypoglos-

sum (NAV) 5 Foramen hypoglossi(Evans, 1993)

Hypoglossal nerve—Nervus hypoglossus(NAV)

Hypoglossal vein—Vena canalis hypoglossi(Evans, 1993)

Hypophyseal fossa—Fossa hypophysealis(NAV)

Hypophysis (NAV)Incisive fissure (this study)—Fissura palatina

(NAV)Incisive foramen (5 palatine fissure)—Fis-

sura palatina (NAV)Incisive incisure of vomer—Vomer, incisura

incisiva (NAV)Incisivomaxillary canal (5 alveolar canal)—

Canalis maxilloincisivus (Evans, 1993)Incisors—Dentes incisivi (NAV)Incudal body—Corpus incudis (NAV)Incudomalleolar joint—Articulation incudo-

mallearis (NAV)Incudostapedial joint—Articulation incudos-

tapedia (NAV)Incus (NAV)Inferior alveolar artery—Arteria alveolaris

inferior (NAV)Inferior alveolar nerve—Nervus alveolaris

inferior (NAV)Inferior alveolar vein—Vena alveolaris in-

ferior (NAV)Inferior (5 ventral) petrosal sinus—Sinus

petrosus ventralis (NAV)Infraorbital artery—Arteria infraorbitalis

(NAV)Infraorbital canal—Canalis infraorbitalis

(NAV)Infraorbital foramen—Foramen infraorbi-

tale (NAV)Infraorbital margin—Margo infraorbitalis

(NAV)Infraorbital nerve—Nervus infraorbitalis

(NAV)Infraorbital vein—Vena infraorbitalis (NAV)Infratemporal crest—Crista infratemporalis

(NAV)

Infratemporal fossa—Fossa infratemporalis(NAV)

Inner lamella of malleus (5 rostral process ofmalleus, part) (Jurgens, 1963)

Inner table of frontal—Os frontale, faciesinterna (NAV)

Intercondyloid (5 odontoid) notch—Inci-sura intercondyloidea (Evans, 1993)

Interdental palate (Andersen, 1912)Interfrontal suture—Sutura interfrontalis

(NAV)Interincisive suture—Sutura interincisiva

(NAV)Intermandibular space—Spatium mandibu-

lae (NAV)Intermaxillary suture—Sutura intermaxillaris

(Evans, 1993) 5 [Rostral part of] suturapalatina mediana (NAV)

Internal acoustic meatus—Meatus acusticusinternus (NAV)

Internal auditory artery (5 labyrinthineartery)—Arteria labyrinthi (NAV)

Internal carotid artery—Arteria carotis in-terna (NAV)

Internal carotid (5 deep petrosal) nerve—Nervus caroticus interna (NAV)

Internal jugular vein—Vena jugularis interna(NAV)

Internal occipital crest of supraoccipital—Osoccipitale, pars squamosa, crista occipitalisinterna (NAV)

Internal surface of maxilla—Os maxillare,facies nasalis (NAV)

Internal surface of nasal—Os nasale, faciesinterna (NAV)

Internal surface of parietal—Os parietale,facies interna (NAV)

Internasal suture—Sutura internasalis(NAV)

Interorbital area of frontal (Miller, 1907)Interpalatine suture (this study)—[Caudal

part of] sutura palatina mediana (NAV)Interparietal—Os interparietalis (NAV)Intersphenoidal synchondrosis—Synchon-

drosis intersphenoidalis (NAV)Intracrural (5 stapedial) foramen—Stapes,

foramen intracrurale (Fleischer, 1973)Jugal—Os zygomaticum (NAV)Jugular foramen—Foramen jugulare (NAV)Jugular incisure—Incisura jugularis (NAV)Juga—Juga alveolaria (NAV)Labyrinthus ethmoidalis (NAV)Lacrimal—Os lacrimale (NAV)


Lacrimal artery—Arteria lacrimalis (NAV)

Lacrimal canal—Canalis lacrimalis (NAV)

Lacrimal duct—Canaliculus lacrimalis(NAV)

Lacrimal fenestra (Wible and Gaudin, 2004)

Lacrimal foramen—Foramen lacrimale(NAV)

Lacrimal sac—Saccus lacrimalis (NAV)

Lacrimoethmoidal suture—Sutura lacri-moethmoidalis (Evans, 1993)

Lacrimomaxillary suture—Sutura lacrimo-maxillaris (NAV)

Lacrimozygomatic suture*—Sutura lacrimo-zygomatica (NAV)

Lambdoid suture—Sutura lambdoidea(NAV); see Occipitointerparietal and Occi-pitoparietal sutures

Lamina basalis of ethmoid—Os ethmoidale,lamina basalis (NAV)

Lamina interna of skull—Cranium, laminainterna (NAV)

Lamina transversalis anterior (Jurgens, 1963)

Laminae lateralis of vomer (Evans, 1993)

Laryngeal prominence*—Cartilago thyroi-dea, prominentia laryngea (Evans, 1993)

Larynx (NAV)

Lateral ligament—Ligamentum lateralis(NAV)

Lateral process of malleus—Malleus, proces-sus lateralis (NAV)

Lateral pterygoid muscle—M. pterygoideuslateralis (NAV)

Lateral ridge of cheekteeth (Andersen, 1912)

Lateral surface of jugal—Os zygomaticum,facies lateralis (NAV)

Lateral surface of petrosal—Os temporale,pars petrosa, facies lateralis (MacIntyre,1972; Wible, 1990)

Lateral (5 vestibular; 5 buccal; 5 facial; 5

labial) surface of teeth—Dentes, faciesvestibularis (5 facialis) (NAV)

Lateral surface of zygomatic arch—Arcuszygomaticus, facies lateralis (NAV)

Left lamina of thyroid—Cartilago thyroidea,lamina sinistra (NAV)

Lenticular process of incus—Incus, processuslenticularis (NAV)

Lesser petrosal nerve—Nervus petrosus mi-nor (NAV)

Levator palpebrae superioris (NAV)

Lingual surface of mandible—Mandibula,facies lingualis (NAV)

Lingula sphenoidalis**—Os basisphenoida-lis, lingula sphenoidalis (Evans, 1993)

Long crus (5 leg) of incus—Incus, cruslongum (NAV)

Longitudinal fissure of brain—Fissura long-itudinalis cerebri (NAV)

Lower tooth row—Arcus dentalis inferior(NAV)

Major palatine artery—Arteria palatina ma-jor (NAV)

Major palatine foramen—Foramen palati-num majus (NAV)

Major palatine nerve—Nervus palatinus ma-jor (NAV)

Malleus (NAV)

Mandible (5 dentary)—Mandibula (NAV)

Mandibular canal—Canalis mandibulae(NAV)

Mandibular condyle (5 condylar process)—Processus condylaris (NAV)

Mandibular foramen—Foramen mandibulae(NAV)

Mandibular nerve—Nervus mandibularis(NAV)

Mandibular (5 lunar) notch (Evans, 1993)—Incisura mandibulae (NAV)

Mandibular symphysis (Evans, 1993)

Manubrium of malleus—Manubrium mallei(NAV)

Masseter muscle—Musculus masseter (NAV)

Masseteric fossa—Fossa masseterica (NAV)

Masseteric line (Evans, 1993)

Masseteric margin of maxilla—Margo mas-setericus (Evans, 1993)

Mastoid angle of parietal—Os parietale,angulus mastoideus (NAV)

Mastoid exposure of petrosal—Processusmastoideus (NAV)

Mastoid foramen—Foramen mastoideum(NAV)

Maxilla—Os maxillare (NAV)

Maxillary artery (5 ramus infraorbitalis)—Arteria maxillaris (NAV)

Maxillary foramen—Foramen maxillare(NAV)

Maxillary nerve—Nervus maxillaris (NAV)

Maxillary recess—Recessus maxillaris (NAV)

Maxillary tuberosity—Tuber maxillae(NAV)

Maxillary vein—Vena maxillaris (NAV)

Maxilloincisive suture—Sutura maxilloinci-siva (NAV)


Maxilloturbinal (5 dorsal nasal concha)—Osconchae nasalis ventralis (NAV)

Meckel’s cartilage (De Beer, 1937; Jurgens,1963)—Cartilago mandibularis (NEV)

Medial pterygoid muscle—Musculus ptery-goideus medialis (NAV)

Medial (5 lingual) surface of teeth—Dentes,facies lingualis (NAV)

Medial surface of zygomatic arch—Arcuszygomaticus, facies medialis (NAV)

Median crest of cricoid—Cartilago cricoidea,crista mediana (NAV)

Median palatine suture—Sutura palatinamediana (NAV)

Median ridge of cheek teeth (Andersen, 1912)Mental foramen—Foramen mentale (NAV)Mental artery—Arteria mentalis (NAV)Mental nerves—Nervi mentales (NAV)Mental vein—Vena mentalis (NAV)Mental surface of mandible—Mandibula,

facies labialis (NAV)Mentalis muscle—Musculus mentalis (NAV)Mesostyle* (Miller, 1907)Metacone** (Miller, 1907)Metaconid** (Miller, 1907)Metastyle* (Miller, 1907)Metastylid* (Slaughter, 1970)Middle nasal meatus—Meatus nasi medius

(NAV)Middle ear—Auris media (NAV)Middle ear ossicles—Ossicula auditus (NAV)Middle meningeal artery—Arteria meningea

media (NAV)Minor palatine artery—Arteria palatina mi-

nor (NAV)Minor palatine foramen (Wible and Rougier,

2000)—Foramen palatinum caudale(NAV)

Minor palatine nerve—Nervus palatinusminor (NAV)

Molars—Dentes molares (NAV)Muscular process of malleus*—Malleus,

processus muscularis (NAV)Muscular process of stapes—Stapes, proces-

sus muscularis (Henson, 1970)Muscular tubercle*—Os occipitale, pars ba-

silaris, tuberculum musculare (NAV)M. digastricus (NAV)M. genioglossus (NAV)M. longus capitis (NAV)M. masseter, pars profunda (NAV)M. masseter, pars superficialis (NAV)M. pterygoideus lateralis (NAV)

M. pterygoideus medialis (NAV)M. rectus capitis ventralis (NAV)M. stapedius (NAV)M. sternomastoideus (Evans, 1993) 5 M.

sternocephalicus, pars mastoidea (NAV)M. temporalis (NAV)M. tensor tympani (NAV)M. thyrohyoideus (NAV)M. zygomaticomandibularis (Storch, 1968)Nasal—Os nasale (NAV)Nasal cavity (5 Nasal fossa)—Cavum nasi

(NAV)Nasal crest of palatine—Os palatinum, crista

nasalis (NAV)Nasal process of premaxilla—Os incisivum,

processus nasalis (NAV)Nasal septum—Septum nasi osseum (NAV)Nasal surface of maxilla—Os maxillare,

facies nasalis (NAV)Nasal vestibule—Vestibulum nasi (NAV)Nasalis muscle 5 Maxillonasolabial muscle

(Evans, 1993)Nasoethmoidal crest of nasal* (Evans, 1993)Nasoethmoidal fossa of nasal* (Evans, 1993)Nasoincisive suture—Sutura nasoincisiva

(NAV)Nasolacrimal canal—Canalis nasolacrimalis

(NAV)Nasolacrimal duct—Ductus nasolacrimalis

(NAV)Nasolacrimal suture*—Sutura nasolacrimalis

(NAV)Nasomaxillary suture—Sutura nasomaxil-

laris (NAV)Nasopalatine duct (Cooper and Bhatnagar,

1976)—Ductus incisivus (NAV)Nasopalatine duct cartilage—Cartilago duc-

tus nasopalatine (Jurgens, 1963)Nasopharyngeal meatus—Meatus nasophar-

yngeus (NAV)Nasopharyngeal surface of pterygoid—Os

pterygoideum, facies nasopharyngea(NAV)

Neck of malleus—Malleus, collum mallei(NAV)

Nerve of pterygoid canal—Nervus canalispterygoidei (NAV)

Nuchal (5 lambdoid) crest—Crista nuchae(NAV)

Nuchal tubercle*—Os occipitalis, pars later-alis, tuberculum nuchale (NAV)

Occipital—Os occipitale (NAV)Occipital artery—Arteria occipitalis (NAV)


Occipital (5 caudal) border of parietal—Osparietale, margo occipitalis (NAV)

Occipital condyle—Condylus occipitalis(NAV)

Occipital emissary vein—Vena emissaria oc-cipitalis (NAV)

Occipital margin of parietal—Os parietale,margo occipitalis (NAV)

Occipitointerparietal suture—Sutura occipi-tointerparietalis (this study) 5 Suturalambdoidea (NAV)

Occipitomastoid suture—Sutura occipito-mastoidea (NAV)

Occipitoparietal suture—Sutura occipitopar-ietalis (Evans, 1993) 5 Sutura lambdoidea(NAV)

Occiput (NAV)

Occlusal surface of teeth—Dentes, faciesocclusalis (NAV)

Oculomotor nerve (5 cranial nerve III)—Nervus oculomotorius (NAV)

Olfactory bulb—Bulbus olfactorius (NAV)

Olfactory nerve (5 cranial nerve I)—Nerviolfactorii (NAV)

Ophthalmic artery—Arteria ophthalmica in-terna (NAV)

Ophthalmic nerve (5 cranial nerve V1)—Nervus ophthalmica (NAV)

Ophthalmic vein—Vena ophthalmica interna(NAV)

Ophthalmic venous plexus—Plexus ophthal-micus (NAV)

Optic canal/foramen—Canalis opticus(NAV)

Optic grooves (Evans, 1993)

Optic nerve (5 cranial nerve II)—Nervusopticus (NAV)

Oral cavity—Cavum oris (NAV)

Orbicular apophysis (Henson, 1961, 1970)

Orbit—Orbita (NAV)

Orbital crest—Crista orbitalis (NAV)

Orbital fissure*—Fissura orbitalis (NAV)

Orbital fossa—Orbita (NAV)

Orbital ligament—Ligamentum orbitale(NAV)

Orbital margin of maxilla—Os maxillare,margo orbitalis (NAV)

Orbital region—Regio orbitalis (NAV)

Orbital surface of frontal—Os frontale, parsorbitalis (NAV)

Orbital surface of jugal—Os zygomaticum,facies orbitalis (NAV)

Orbital surface of lacrimal—Os lacrimale,facies orbitalis (NAV)

Orbitosphenoid—Os presphenoidale, ala or-bitalis (NAV)

Orbitosphenoidal crest—Crista orbitosphe-noidalis (NAV)

Orbitotemporal canal* (Rougier et al., 1992;Wible et al., 2004) 5 Sinus canal (Gregory,1910; McDowell, 1958)

Ossa cranii (NAV)

Ossa faciei (NAV)

Osseus lamina of mallei (Evans, 1993) 5

Lamina (Henson, 1970)

Osseous nasal aperture—Apertura nasi ossea(NAV)

Osseous nasal septum—Septum nasi osseum(NAV)

Otic ganglion—Ganglion oticum (NAV)

Outer lamella of malleus (5 rostral process ofmalleus, part) (Jurgens, 1963) 5 Tympanicplate of anterior process (Henson, 1970)

Oval window—Fenestra vestibuli (NAV)

Palatine—Os palatinum (NAV)

Palatine canal—Canalis palatinus (NAV)

Palatine cartilage—Cartilago palatini (Jur-gens, 1963)

Palatine process of maxilla—Maxillare, pro-cesses palatinus (NAV)

Palatine process of premaxilla*—Os incisi-vum, processus palatinus (NAV)

Palatine sulcus—Sulcus palatinus (NAV)

Palatine surface of palatine—Os palatinum,facies palatina (NAV)

Palatoethmoidal suture—Sutura palatoeth-moidalis (NAV)

Palatolacrimal suture—Sutura palatolacri-malis (NAV)

Palatomaxillary suture—Sutura palatomaxil-laris (Evans, 1993) 5 Sutura palatinatransversa (NAV)

Paracondylar process of exoccipital—Proces-sus paracondylaris (NAV)

Paracone** (Miller, 1907)

Paraconid** (Miller, 1907)

Parachordal plate (5 central stem) (DeBeer,1937)

Paraflocculus of cerebellum—Paraflocculus(NAV)

Parastyle* (Miller, 1907)

Paries nasi (Jurgens, 1963)

Parietal—Os parietale (NAV)

Parietal region—Regio parietalis (NAV)


Parietointerparietal suture—Sutura parie-tointerparietalis (Evans, 1993)

Paroccipital process (Wible and Gaudin,2004)—Processus mastoideus (Schaller,1992)

Pars canalicularis of petrosal (Wible, 1990;Wible et al., 1995, 2001)

Pars cochlearis of petrosal (Wible, 1990;Wible et al., 1995, 2001)

Pars incisiva of mandible—Mandibula, parsincisiva (NAV)

Pars orbitalis of frontal—Os frontale, parsorbitalis (NAV)

Perbullar canal* (Wible, 1986)

Perilymphatic duct—Ductus perilymphaticus(NAV)

Permanent teeth—Dentes permanentes(NAV)

Perpendicular lamina of ethmoid—Os eth-moidale, lamina perpendicularis (NAV)

Perpendicular process of palatine—Os pala-tinum, lamina perpendicularis (NAV)

Petrosal (5 petrous temporal)—Os tempor-ale, pars petrosa (NAV)

Petro-occipital (5 petrobasilar) canal*—Ca-nalis petrooccipitalis (NAV)

Pharyngeal tubercle of basioccipital—Osbasioccipitalis, tuberculum pharyngeum(NAV)

Piriform fenestra (5 foramen lacerum) 5

Pyriform fenestra (McDowell, 1958)—Fo-ramen lacerum (NAV)

Planum parietale (NAV)

Pleurethmoid (Jurgens, 1963)

Palatomaxillary suture—Sutura palatomaxil-laris (NAV)

Pontine impression of basioccipital—Os oc-cipitalis, pars basilaris, impressio pontina(NAV)

Porus acusticus internus (NAV)

Postdental palate (Andersen, 1912)

Posterior auricular artery—Arteria auricu-laris caudalis (NAV)

Posterior basicochlear (5 basicapsular) com-missure (De Beer, 1937)—Syncondrosispetro-occipitalis (NAV)

Posterior cornu of hyoid (Sprague, 1943)—Cornu majus (NAV) 5 Cornu branchiale(Jurgens, 1963)

Posterior crus (5 leg) of ectotympanic—Annulus tympanicus, crus posterior(NAV)

Posterior (5 caudal) crus (5 leg) of stapes—Stapes, crus caudale (NAV)

Posterior ligament of incus—Ligamentusincudis posterius (NAV)

Posterior mental foramen: see Mental fora-men

Posterior semicircular canal—Canalis semi-circularis posterior (NAV)

Posterobasal ledge of cheek teeth (Andersen,1912)

Postglenoid foramen (5 retroarticular fora-men)—Foramen retroarticulare (NAV)

Postglenoid process (5 retroarticular pro-cess)—Processus retroarticulare (NAV)

Postglenoid (5 retroarticular; 5 capsulopar-ietal emissary) vein—Vena emissaria for-aminis retroarticularis (NAV)

Postorbital area of frontal (Andersen, 1912;Miller, 1907)

Postorbital ligament—Ligamentum orbitale(NAV)

Postorbital process—Os frontale, processuszygomaticus (NAV)

Postpalatine torus (Novacek, 1986)Posttemporal canal* (Wible, 1989; Rougier et

al., 1992)Posttemporal foramen (Notch)* (Rougier et

al., 1992)Posttympanic process (Kielan-Jaworwoska,

1981; Novacek, 1986)—Processus retro-tympanicus (NAV)

Prearticular (5 gonial) (Goodrich, 1930)Prefacial (5 suprafacial) commissure (De

Beer, 1937; Jurgens, 1963)Premaxilla—Os incisivum (NAV)Premolars—Dentes praemolares (NAV)Preorbital area of frontal—Os frontale, pars

nasalis (NAV)Presphenoid—Os presphenoidale, corpus

(NAV)Primary facial foramen (Wible, 1990; Wible

and Hopson, 1993)Promontorium of petrosal (Evans, 1993)Protocone** (Miller, 1907)Protoconid** (Miller, 1907)Protostylid* (Slaughter, 1970)Pterygoid—Os pterygoideum (NAV)Pterygoid canal—Canalis pterygoideus

(NAV)Pterygoid process of basisphenoid (Evans,

1993)Pterygoid process of maxilla—Os maxillare,

processus pterygoideus (NAV)


Pterygopalatine fissure (this study)

Pterygopalatine fossa—Fossa pterygopala-tina (NAV)

Pterygopalatine ganglion—Ganglion ptery-gopalatinum (NAV)

Pterygopalatine nerve—Nervus pterygopala-tinus (NAV)

Pterygopalatine surface of pterygoid—Ospterygoideum, facies pterygopalatina(NAV)

Pterygopalatine suture—Sutura pterygopala-tina (NAV)

Pterygosphenoid suture—Sutura pterygo-sphenoidalis (NAV)

Ramus inferior of stapedial artery (Wible,1987)

Ramus infraorbitalis (Wible, 1987)

Ramus mandibularis (Wible, 1987)

Ramus supraorbitalis (Wible, 1987)

Ramus of mandible—Ramus mandibulae(NAV)

Ramus superior of stapedial artery (Wible,1987)

Ramus temporalis of stapedial artery (Wible,1987)

Regio dorsalis nasi (NAV)

Regio frontalis (NAV)

Regio intermandibularis (NAV)

Regio maxillaris (NAV)

Regio naris (NAV)

Regio orbitalis (NAV)

Regio parietalis (NAV)

Regio temporalis (NAV)

Regio zygomatica (NAV)

Reichert’s cartilage (5 second pharyngealarch) (De Beer, 1937; Jurgens, 1963)

Retromolar space 5 Retromolar fossa (Hiattand Gartner, 1987)

Right lamina of thyroid—Thyroid cartilage,lamina dextra (NAV)

Rostral axis (Andersen, 1912)

Rostral alar foramen*—Foramen alare ros-trale (NAV)

Rostral (5 frontal) border of parietal—Osparietale, margo frontalis (NAV)

Rostral clinoid process—Os presphenoidale,processus clinoideus rostralis (NAV)

Rostral cornu of thyroid—Cartilago thyroi-dea, cornu rostralis (NAV)

Rostral cranial fossa of frontal—Os frontale,facies interna, fossa cranii rostralis (Evans,1993)

Rostral entotympanic—Rostrales entotym-panicum (Klaauw, 1922)

Rostral process of ethmoturbinal (this study)5 ‘‘Anterior tip’’ of ethmoturbinal (Jur-gens, 1963)

Rostral (5 anterior) process of malleus—Malleus, processus rostralis (NAV) 5

Processus gracilis (outer lamella; Jurgens,1963)

Rostral (5 facial) process of maxilla—Osmaxillare, facies facialis (NAV)

Rostral septal branch of major palatineartery—Rami septi rostrales (Evans, 1993)

Rostral thyroid notch—Incisura thyroidearostralis (NAV)

Rostromedial process of pterygoid (thisstudy)

Rostrum (NAV)Rostrum of presphenoid*—Os presphenoi-

dale, rostrum sphenoidale (NAV)Root of teeth—Dentes, radix dentis (NAV)Round window—Fenestra cochleae (NAV)Saccule—Sacculus (NAV)Sagittal (5 dorsal) border of parietal—Os

parietale, margo sagittalis (NAV)Sagittal crest—Crista sagittalis externa

(NAV)Sagittal part of vomer (Evans, 1993)Sagittal suture—Sutura sagittalis (NAV)Second pharyngeal arch (5 Reichert’s carti-

lage 5 Hyoid arch (Sprague, 1943)—Arcuspharyngeus secundus (NEV)

Secondary facial foramen (Wible, 1990;Wible and Hopson, 1993)

Secondary tympanic membrane—Membranatympani secundaria (NAV)

Sella turcica (NAV)Septal branch of caudal nasal nerve (5

Nasopalatine nerve) (Evans, 1993)—Ner-vus nasopalatinus (NAV)

Septal cartilage—Cartilago septi nasi (NAV)Septal process of nasal—Os nasale, processus

septalis (NAV)Semicircular canal—Canalis semicircularis

(NAV)Shaft (5 neck) of teeth—Dentes, collum

dentis (NAV)Short crus (5 leg) of incus—Incus, crus breve

(NAV)Sigmoid sinus—Sinus sigmoideus (NAV)Sinciput (NAV)Sixth pharyngeal arch—Arcus pharyngeus

sextus (NEV)


Sphenoethmoid lamina of palatine—Os pa-latinum, lamina sphenoethmoidalis (NAV)

Sphenofrontal suture—Sutura sphenofronta-lis (NAV)

Sphenoidal angle of parietal—Os parietale,angulus sphenoidalis (NAV)

Sphenoidal crest—Crista sphenoidalis (NAV)Sphenoidal incisure of vomer—Incisura

sphenoidalis (NAV)Sphenorbital fissure (Novacek, 1986)—Fis-

sura orbitalis + foramen rotundum +foramen alare rostrale + foramen alareparvum (NAV)

Sphenoidal process of palatine—Os palati-num, processus sphenoidalis (NAV)

Sphenoidal sinus—Sinus sphenoidalis (NAV)Sphenomaxillary suture*—Sutura spheno-

maxillaris (NAV)Spheno-occipital synchondrosis—Synchon-

drosis spheno-occipitalis (NAV)Sphenopalatine artery—Arteria sphenopala-

tina (NAV)Sphenopalatine foramen—Foramen spheno-

palatinum (NAV)Sphenopalatine suture—Sutura sphenopala-

tina (NAV)Sphenopalatine vein—Vena sphenopalatina

(NAV)Sphenoparietal suture—Sutura sphenoparie-

talis (NAV)Sphenosquamosal suture—Sutura sphenos-

quamosa (NAV)Spinal cord—Medulla spinalis (NAV)Spiral tract of minute foramina—Tractus

spiralis foraminosus (NAV)Squama frontalis of frontal (NAV)Squamosal—Os temporale, pars squamosa

(NAV)Squamosofrontal suture*—Sutura squamo-

sofrontalis (NAV)Squamosomastoid suture—Sutura squamo-

somastoidea (NAV)Squamous border of parietal—Os parietale,

margo squamosus (NAV)Stapedial artery—Arteria stapedia (Tandler,

1899; Wible, 1984, 1987)Stapedius muscle—Musculus stapedius

(NAV)Stapes (NAV)Stylar (5 labial) shelf (Slaughter, 1970)Stylid* (Slaughter, 1970)Styliform process of ectotympanic (Henson,

1970)

Stylohyoid—Stylohyoideum (NAV)Stylohyoid cartilage—Cartilago stylohyoidea

(NAV)Stylomastoid artery—Arteria sylomastoidea

(NAV)Stylomastoid foramen*—Foramen stylomas-

toideum (NAV)Stylomastoid notch—Foramen stylomastoi-

deum (NAV)Subarcuate fossa—Fossa subarcuata (NAV)Sulci of brain—Sulci cerebri (NAV)Sulcus for capsuloparietal emissary vein—

Transverse sulcus of temporal bone(Evans, 1993)

Sulcus for inferior petrosal sinus—Sulcussinus petrosa ventralis (NAV)

Sulcus for venous transverse sinus*—Sulcussinus transversi (NAV)

Sulcus lacrimalis (NAV)Sulcus medullae oblongatae (NAV)Sulcus septi nasi (Evans, 1993)—Sulcus

vomeris (septalis) (NAV)Sulcus tympanicus (NAV)Suprameatal bridge 5 Dorsal boundary of

external acoustic meatus (Evans, 1993)Supraoccipital—Os occipitalis, squama occi-

pitalis (NAV)Supraorbital margin—Margo supraorbitalis

(NAV)Superior petrosal sinus—Sinus petrosus dor-

salis (NAV)Sutura intermandibularis (NAV)Sutura squamosa (NAV)Suturae capitis (NAV)Syndesmosis tympanostapedia (NAV)Tectum nasi (Jurgens, 1963)Tegmen tympani (NAV)Temporal canal (Evans, 1993)Temporal fossa—Fossa temporalis (NAV)Temporal line—Linea temporalis (NAV)Temporal process of jugal—Os zygomati-

cum, processus temporalis (NAV)Temporal region—Regio temporalis (NAV)Temporomandibular joint—Articulatio tem-

poromandibularis (NAV)Tendon of tensor tympani muscle (Jurgens,

1963)Tensor tympani muscle—Musculus tensor

tympani (NAV)Tentorial process*—Processus tentoricus

(NAV)Third pharyngeal arch—Arcus pharyngeus

tertius (NEV)


Thyrohyoid—Thyrohyoideum (NAV)

Thyrohyoid articulation—Articulatio thyro-hyoidea (NAV)

Thyrohyoid cartilage—Cartilago thyrohyoi-dea (NAV)

Thyroid cartilage—Cartilago thyroidea(NAV)

Thyroid fissure—Fissura thyroidea (NAV)

Tip of dental cusp—Dentes, apex cuspidis(NAV)

Tracheal rings—Cartilagines tracheales(NAV)

Transverse crest of petrosal—Crista trans-versa (NAV)

Transverse palatine suture—Sutura palatinatransversa (NAV)

Transverse sinus—Sinus transversus (NAV)

Tribosphenic molar (Slaughter, 1970)

Trigeminal ganglion—Ganglion trigeminale(NAV)

Trigeminal nerve (5 cranial nerve V)—Nervus trigeminus (NAV)

Trochlear nerve (5 cranial nerve IV)—Nervus trochlearis (NAV)

Tubal cartilage—Cartilago tubae auditivae(NAV)

Tympanic (5 middle ear) cavity—Cavumtympani (NAV)

Tympanic membrane—Membrana tympani(NAV)

Tympanic surface of petrosal—Os temporale,pars petrosa, facies tympanica (Evans,1993)

Tympanohyoid (5 tympanohyal)—Tympa-nohyoideum (NAV)

Tympanostyloid ligament (Sprague, 1943;Jurgens, 1963)

Upper tooth row—Arcus dentalis superior(NAV)

Utricle—Utriculus (NAV)

Vagus nerve (5 cranial nerve X)—Nervusvagus (NAV)

Vascular angle of parietal (this study)

Vascular foramen of lacrimal (this study)

Vena diploetica magna (Hyrtl, 1853, 1854)

Ventral border of mandible—Mandibula,margo ventralis (NAV)

Ventral condyloid fossa—Fossa condylarisventralis (NAV)

Ventral intraoccipital synchondrosis (Evans,1993)—Synchondrosis intraoccipitalis ba-silateralis (NAV)

Ventral nasal concha (5 maxilloturbinate)—Concha nasalis ventralis (NAV)

Ventral nasal meatus—Meatus nasi ventralis(NAV)

Ventral vestibular area of petrosal—Areavestibularis inferior (NAV)

Ventrocaudal process of arytenoid (thisstudy)

Vermiform impression of supraoccipital—Osoccipitale, pars squamosa, impressio ver-mialis (NAV)

Vertebral artery—Arteria vertebralis (NAV)Vestibular aqueduct—Apertura externa

aqueductus vestibuli (NAV)Vestibular fossula (MacPhee, 1981)Vestibular nerve—Nervus vestibularis

(NAV)Vestibulocochlear nerve (5 cranial nerve

VIII)—Nervus vestibulocochlearis (NAV)Vomer (NAV)Vomeroethmoidal suture—Sutura vomer-

oethmoidalis (NAV)Vomeroincisive suture*—Sutura vomeroinci-

siva (NAV)Vomeromaxillary suture—Sutura vomero-

maxillaris (NAV)Vomeronasal organ—Organum vomerona-

sale (NAV)Vomeropalatine suture—Sutura vomeropala-

tina dorsalis (NAV)Vomerosphenoidal suture—Sutura vomero-

sphenoidalis (NAV)Wings of vomer—Alae vomeris (NAV)Yoke—Jugum sphenoidale (NAV)Zygoma—Arcus zygomaticus (NAV)Zygomatic arch—Arcus zygomaticus (NAV)Zygomatic process of maxilla—Os maxillare,

processus zygomaticus (NAV)Zygomatic process of squamosal—Os tem-

porale, pars squama, processus zygomati-cus (NAV)

Zygomaticomaxillary suture—Sutura zygo-maticomaxillaris (NAV)


APPENDIX 2

LIST OF ANATOMICAL ABBREVIATIONS USED

IN FIGURES

ac alveolar canalalec anterior leg of the ectotympanicalst anterior leg of stapesalv ala vomerisamf anterior mental foramenan angle of mandibleao alae orbitales of sphenoid complexapf accessory palatine foraminaaplin attachment of posterior ligament of

incusapp apex parties petrosaas alisphenoidasc anterior semicircular canalasu alar sulcus of alisphenoidat alae temporales of sphenoid complexattm attachment of m. tensor tympaniav aqueductus vestibulibcc posterior basicochlear commissurebcf basicochlear fissurebo basioccipitalbs basisphenoidbst base of stapesC upper caninec lower canine‘‘c’’ column of bone on lateral side of

ethmoturbinalcc cochlear canaliculusccr conchal crest of maxillaccthy caudal cornu of thyroidcehy ceratohyoidcf carotid foramenCju upper canine jugumcllo caudolateral lobe of parietalcon mandibular condylecor coronoid process of mandiblecp crista paroticacppt caudal process of pterygoidcrarra cricoarytenoid articulationcrc crus communecrga crista gallicrif cribriform foraminacs carotid sulcus of basisphenoidct crista transversa of petrosalctpp caudal tympanic process of petrosalcty crista tympanicacv crest of vomercvma caudoventral margin of parietaldC deciduous upper canine

dc deciduous lower caninedI1 deciduous first upper incisordi1 deciduous first lower incisordI2 deciduous second upper incisordi2 deciduous second lower incisordlcr dorsal lamina of cricoiddP1 deciduous first upper premolardp1 deciduous first lower premolardP2 deciduous second upper premolardp2 deciduous second lower premolards dorsum sellaeeam external acoustic meatusec ectotympanicecptp ectopterygoid processef ethmoidal foramenein unnamed round eminence of incusen rostral entotympanicent-III endoturbinate IIIeo exoccipitalephy epihyoidetan epitympanic angle of parietaletfo ethmoidal fossaeeth ethmoidethtu ethmoturbinaletma epitympanic margin of parietaletwas epitympanic wing of alisphenoidfai foramen acusticum inferiusfam incudal facet for head of malleusfas foramen acusticum superiusfc fenestra cochleaefcb fossa cerebellarisfctn foramen for the chorda tympani nervefdv foramen for frontal diploic veinfh fossa hypophysialisfi fossa incudisfifr facies interna of frontalfipa facies interna of parietalfm foramen magnumfo foramen ovalefofr facies orbitalis of frontalfr frontalfran frontal angle of parietalfrma frontal margin of parietalfrp frontal process of maxillafrt foramina for rami temporalesfs facial sulcus of petrosalfv fenestra vestibuligc anterior groove of upper caninegf glenoid fossaham hamulus pterygoideushF hiatus Fallopiihf hypoglossal foramenhm head of malleus


hppal horizontal process of palatinehst head of stapesI1 first upper incisori1 first lower incisorI2 second upper incisori2 second lower incisoriam internal acoustic meatusicf intercrural foramen of stapesif incisive fissureiiv incisura incisiva of vomerim infraorbital marginimdi impressiones digitataein incusioc infraorbital canaliocr internal occipital crestiof infraorbital foramenip interparietalisv incisura sphenoidalis of vomeritf inner table of frontalja jugajf jugular foramenji jugular incisurejsp yoke or jugum sphenoidaleju jugallac lacrimallacf lacrimal foramenlacfe lacrimal fenestralc lateral cusp of cheek teethlcin long crus of incuslm lamina of malleuslp lenticular process of incuslpm lateral process of malleuslppt lateral process of pterygoidlsp lingula sphenoidalislthy lamina of thyroidM1 first upper molarm1 first lower molarM2 second upper molarm2 second lower molarm3 third lower molarma malleusmaan mastoid angle of parietalmam manubrium of malleusmanf mandibular foramenmapf major palatine foramenmas mandibular symphysismc medial cusp of cheek teethmccr median crest of cricoidmdnm middle dorsal nasal meatusme mastoid exposure of petrosalmf mastoid foramenmpf minor palatine foramenmpst muscular process of stapes

ms mental surfacemx maxillamxf maxillary foramenmxtu maxillary tuberosityna nasalnas nasal septumnalacc nasolacrimal canalnm neck of malleusnmf notch for mastoid foramennspof notch of sphenorbital fissurenst neck of stapesnuc nuchal crestoam orbicular apophysis of malleusoc occipital condyleocma occipital margin of parietalomj occipito-mastoid jointopc optic canalos orbitosphenoidP1 first upper premolarp1 first lower premolarP3 third upper premolarp3 third lower premolarP4 fourth upper premolarp4 fourth lower premolarpa parietalpal palatinepalp palatine process of maxillapc palatine canalpcp paracondylar processpfc prefacial commissurepgf postglenoid foramenpgp postglenoid processpif piriform fenestraplec posterior leg of ectotympanicplst posterior leg of stapespmf posterior mental foramenpmx premaxillapnfr pars nasalis of frontalpof postorbital foramenpop postorbital processpp paroccipital process of petrosalpppal perpendicular process of palatinepr promontorium of petrosalps presphenoidpsc posterior semicircular canalpt pterygoidptc pterygoid canalptmx pterygoid process of maxillaptp posttympanic process of squamosalptpbs pterygoid process of basisphenoidptpfi pterygopalatine fissureptpmx pterygoid process of maxillar1M1 anterior root of first upper molar


r2M1 posterior root of first upper molarrc posteromedial ridge of upper caninercfo rostrocranial fossarcp rostral clinoid processrcthy rostral cornu of thyroidrM2 roots of second upper molarrmppt rostromedial process of pterygoidrpm rostral process of malleussaf subarcuate fossasc sutura coronalisscev sulcus for capsuloparietal emissary veinscin short crus of incussf stapedial fossasff secondary facial foramensffr squama frontalis of frontalsfl sutura frontolacrimalissfm sutura frontomaxillarissfn sutura frontonasalissif sutura interfrontalissimx sutura intermaxillarissin sutura internasalissiocbl synchondrosis intraoccipitalis basila-

teralissipal sutura interpalatinasisp synchondrosis intersphenoidalissmi sutura maxilloincisivasmn stylomastoid notchsmo sulcus medullae oblongataesnamx sutura nasomaxillarissnm sutura nasomaxillarisso supraoccipitalsoipa sutura occipitointerparietalissopa sutura occipitoparietalisspamx sutura palatomaxillarisspan sphenoidal angle of parietalspc sphenoidal crestspetl sphenoethmoid laminaspf sphenopalatine foramen

spip sutura parietointerparietalisspof sphenorbital fissurespsi sphenoidal sinussq squamosalsqa squama of squamosalsqma squamosal margin of parietalsrt sulci for rami temporalesss sutura sagittalissspal sutura sphenopalatinasspar sutura sphenoparietalissspo synchondrosis spheno-occipitalissspsq sutura sphenosquamosassq sutura squamosast sulcus tympanicussthy stylohyoidsts sulcus for transverse sinusstz sutura temporozygomaticaSut sutureSyn synchondrosisszmx sutura zygomaticomaxillaristc temporal canalth tympanohyoidthcra thyrocricoid articulationthhy thyrohyoidthy thyroid cartilagethyfi thyroid fissuretl temporal linett tegmen tympanittf tensor tympani fossav vomerva vascular angle of parietalveim vermiform impressionvflac vascular foramen of lacrimalvlacr ventrolateral arc of cricoidvnc ventral nasal conchavnm ventral nasal meatuszpmx zygomatic process of maxillazpsq zygomatic process of squamosal


on the cranial osteology of chiroptera. i. pteropus

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