1 osteology of cranial bones rt(67) dr. rahul tiwari
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OSTEOLOGY OF CRANIAL BONES
PRESENTED BYDr. RAHUL TIWARI
1ST YEAR MDS - PG StudentDEPT. OF ORAL & MAXILLOFACIAL SURGERY
SIBAR INSTITUTE OF DENTAL SCIENCES
GOOD AFTERNOON
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CONTENTS INTRODUCTION CRANIAL BONES
EMBRYOLOGY ANATOMY VARIATIONS
APPLIED CLINICAL ASPECTS SURFACE ANATOMY AND ITS IMPORTANCE DEVELOPMENTAL DISTURBANCES
CONCLUSION
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INTRODUCTION Osteology- The branch of anatomy that
studies the bones of the skeleton. Cranial- Of or relating to the cranium
which encloses the brain. Bones- Rigid connective tissue that
makes up the skeleton. Skeleton- The hard structure (bones and
cartilages) that provides a frame for the body.
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EMBRYOLOGY Cranium is formed from:
● Paraxial mesoderm ● Neural crest
Cranium development occurs in Neurocranium forms the bones of the cranial base and cranial vault
and can be divided into membranous neurocranium and cartilaginous neurocranium
Bony cranium is formed by either of 2 mechanisms: ● Intramembranous ossification ● Endochondral ossification
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MEMBRANOUS NEUROCRANIUMGerm Layer
Portions of Neurocranium
Adult Structure
Ossification
Neural crest
Main portion of the roof and lateral sides of the cranial vault
Frontal bone
Squamous portion ofthe temporal bone
Intramembranous
Paraxialmesoderm
Main portion of the roof and lateral sides of the cranial vault
Parietal bone
Occipital bone(intraparietal portion)
Intramembranous
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CARTILAGINOUS NEUROCRANIUM
Germ Layer
Portions of Neurocranium
Adult Structure Ossification
Neural crest
Prechordal
Anterior to the sella turcica
Ethmoid
Sphenoid
Endochondral
Paraxialmesoderm
Chordal
Posterior to the sella turcica
Petrous portion of the temporal bone
Mastoid process of thetemporal bone
Occipital bone
Endochondral
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INTRAMEMBRANOUS OSSIFICATION Intramembranous or endesmal
ossification occurs in the connective tissue of the primary (membrane) bones.
The future bones are first formed as connective tissue membranes, that are replaced with bony tissue They include certain flat bones of the skull and some of the irregular bones.
The osteoblasts migrate to the membranes and deposit bony matrix around themselves.
As a result of osteoblastic activity appear
points (centers) or nuclei of ossification.
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ENDOCHONDRAL OSSIFICATIONEndochondral or enchondral ossification involves the replacement of hyaline cartilage with bony tissue. Most of the bones of the skeleton are formed in this manner
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ENDOCHONDRAL OSSIFICATION
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THE PRIMORDIAL CARTILAGES OF THE CHONDROCRANIUM AND THEIR DERIVATIVES
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MEMBRANE BONES AT 9 & 12 WEEKS
Brown-Pharyngeal arch mesenchyme for viscerocranium
Red- Head mesenchyme for neurocranium
Blue- Cartilage from pharyngeal arches for viscerocranium and neck cartilages.
Purple- Cartilage from somite sclerotomes and neural crest anteriorly for base of neurocranium.
Brown & red- Intramembranous ossification
Purple & blue- Endochondral ossification
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SKULL OF NEWBORN
Fontanelle Time of Closure
Anterior fontanelle (bregma) 4–26 months Posterior fontanelle (lambda) 1–2 months
Sphenoidal fontanelle (pterion) 2–3 months Mastoid fontanelle (asterion) 12–18 months
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POSTNATAL GROWTH Growth of the vault is rapid during the
first year and then slower to the seventh.
Growth in breadth occurs at the sagittal, sphenofrontal, sphenotemporal and occipitomastoid sutures and petro-occipital cartilaginous joints.
Growth in height occurs at the frontozygomatic, pterion and asterion.
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POSTNATAL GROWTH During this period fontanelles are closed by
ossification of the bones around them, but separate centres may convert them into sutural bones.
At birth the vault is unilaminar. Tables and intervening diploe appear about the fourth year, with maximal differentiation at about 35 years, when diploic veins are prominent in radiograms.
Growth ceases by 15 yrs in male and 17.5 yrs in males
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THE SECTIONAL ANATOMY OF THE SKULL
Figure 7.4a
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CALVARIA
Frontal bone - 1
Parietal bone - 2
Temporal bone - 2
Occipital bone - 1
Sphenoid bone - 1
Ethmoid bone - 1
-Unpaired bones:
frontal bone, ethmoid bone, sphenoid bone, occipital bone
-Paired bones:
temporal bone parietal bone
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ARTICULATION
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ARTICULATIONS. NO.
Bone Single
Paired
Articulates with
1 Frontal X Parietal, sphenoid, zygomatic, maxilla, ethmoid, nasal, lacrimal
2 Parietal X Frontal, parietal, temporal, occipital, sphenoid
3 Temporal
X Parietal, occipital, sphenoid, zygomatic, mandible
4 Occipital X Parietal, temporal, sphenoid, and atlas (C1)
5 Sphenoid
X Frontal, parietal, temporal, occipital, zygomatic, maxilla, ethmoid,palatine, vomer
6 Ethmoid X Frontal, sphenoid, maxilla, palatine, vomer, nasal, lacrimal, inferiornasal concha
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FRONTAL BONE
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FRONTAL BONE
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FRONTAL BONE
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Characteristics Part
sOssification
Comments
Contains the frontal & paranasal sinusesHas two primary centers that ossify alongfrontal suture (metopic) in the 2nd yearHelps form the foramencecum, which allows passage of an emissaryvein that connects to the superior sagittal sinus There is 1 frontal bone
Squamous part
For all 3 parts: intramembranous
The largest part of the frontal boneForms the majority of the foreheadForms the supraorbital margin and the superciliary arch. The zygomatic process of the frontal bone extends from the posterior part of supraorbital marginArachnoid foveae—depressionscaused by arachnoid granulationsthat push on the Dura mater,causing bone resorption on theendocranial surface
Orbital part
Forms the roof of the orbit and floor of the anterior cranial fossa
Nasal part
The trochlea of the orbit articulateswith the orbital portionArticulates with the nasal bonesand the frontal process of themaxilla to form the root of the nose
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OCCIPITAL BONE
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Characteristics Part
sOssification
Comments
Forms the posterior part of the cranial vault articulates with the atlas The squamous andlateral portionsnormally ossifytogether by year 4 The basilar portion unites to this sectionat year 6There is 1 occipital Bone
Squamous portion
Intramembranous
Articulates with the temporal and parietal bonesArticulates with the largest portion of the occipital bone Located posterior and superior to foramen magnumHas the external occipital protuberance (more pronouncedin males) Has the superior and the inferior nuchal linesHas grooves on the internal surface for 3 of the sinuses forming the confluence of the sinuses (the superior sagittal andthe right and left transverse sinuses)The depression superior to the transverse sinus is for the occipital lobes of the brain The depression inferior to the transverse sinus is for the Cerebellum
Lateral portion
Endochondral
Articulates with the temporal Bone Is the portion lateral to the foramen magnum Has the occipital condyles that articulate with the atlasContains the hypoglossal canal Forms a portion of the jugular foramen
Basilar portion
Endochondral
Articulates with the petrous part of the temporal and the sphenoid bones Is the portion immediately anterior to the foramen magnum Pharyngeal tubercle is part of the basilar portion that provides attachment for the superior Constrictor Internal surface of the basilar portion is called the clivus, and part of the brainstem lies against it
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SPHENOID BONE
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SPHENOID BONE
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SPHENOID BONE
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SPHENOID BONECharacteristics
Parts
Ossification
Comments
Forms the majority of the middle portion of the cranial base & fossa contains the sphenoid paranasal sinus. There is 1 sphenoid bone
Body
Endochondral ossification
The center of the sphenoidAnterior portion of the body helps form part of the nasal cavitySuperior part of the body, known as the sella turcica, is saddle shaped and possesses the anterior and posterior clinoid processes Hypophyseal fossa, the deepest part of the sella turcica, houses the pituitary gland Dorsum sellae is a square-shaped part of the bone that lies posterior to the sella turcica Clivus is the portion that slopes posterior to the body contains the sphenoidparanasal sinuses Lateral portion of the body iscovered by the cavernous sinusOptic canal is found in the body ofthe sphenoid
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Pterygoid process
Intramembranous ossification
Arises from the inferior surface of the body.There are 2 pterygoid processes, Each has a:● Lateral pterygoid plate ● Medial pterygoid plate Pterygoid hamulus extends from the medial pterygoid plate Two canals are associated with the pterygoid process: ●Pterygoid canal ● Pharyngeal canal
Lesser wing
Endochondral ossification
Extends laterally and anteriorly from the superior portion of thesphenoid body Separated from the greater wing bythe superior orbital fissure
Greater wing
Endochondral and intramembranous ossification
Extends laterally and anteriorly from the posterior portion of the body of the sphenoidEndocranial portion helps form a large part of the middle cranial fossaLateral portion is the infratemporal surfaceAnterior portion lies in the orbitContains 3 foramina:● Foramen spinosum● Foramen rotundum● Foramen ovale
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THE ETHMOID
Figure 7.9
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ETHMOID BONE
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ETHMOID BONE
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ETHMOID BONE
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ETHMOID BONE
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Characteristics Part
Ossification
Comments
A porous bone that forms the major portion of the middle part of the face between the orbits Helps form the orbit, nasal cavity, nasal septum, andanterior cranial fossa There is 1 ethmoid bone
Perpendicular plate
Endochondral
A flat plate that descends from the cribriform plate to form part of the nasal septumArticulates with the vomerInferiorly
Cribriform plate
A horizontal bone that forms thesuperior surface of the ethmoidContains numerous foramina forthe olfactory nerveCrista galli is a vertical plate that extends superiorly from thecribriform plate providing attachment for the falx cerebri of the meninges Associated with a small foramen cecum
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ETHMOID BONEEthmoid labyrinth
The largest part of the ethmoid Bone Descends inferiorly from the cribriform plate Ethmoid paranasal sinuses are located within the ethmoid Labyrinth Ethmoid labyrinth forms 2 major structures within the nasal cavity: ● Superior nasal concha● Middle nasal concha Ethmoid bulla is the large elevation of bone located by the middle ethmoid paranasal sinusesUncinate process is a curved piece of bone Between the uncinate process and the ethmoid bulla is the hiatus semilunaris
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THE TEMPORAL BONES
Figure 7.7
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TEMPORAL BONE
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TEMPORAL BONE
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TEMPORAL BONE
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Characteristics
Parts
Ossification
Comments
Squamous part
Intramembranous
The largest portion of the bone Three portions to the squamous part: ● Temporal● Zygomatic process● Glenoid fossaTemporal portion is the thin large area on the squamous part of the temporalOn the internal surface of the temporal portion lies a groove for the middle meningeal a. The zygomatic process extends laterally and anteriorly from the squamous portion; it articulates with the temporal process of thezygomatic bone to make the zygomatic archGlenoid fossa is inferior and medial to the zygomatic process; it articulates with the mandibular condyle, forming the temporomandibular joint
Tympanic part
Intramembranous
A plate of bone forming the anterior, posterior, and inferior portions of the external acoustic meatusAnterior part forms the posteriorportion of the glenoid fossa
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Petrous part
Endochondral
Forms the solid portion of bone The auditory and vestibular apparatuses are located within the petrous part Helps to separate the temporal and the occipital lobes of the brain It extends anteriorly and medially The medial part articulates with the sphenoid bone to form the foramen lacerum Internal acoustic meatus is observed on the medial side of the petrous part Carotid canal lies on the inferior part of the petrous part Petrotympanic fissure lies between the petrous part of the temporal bone and the tympanic part of the temporal bone On the medial portion of the petrous part lie grooves for the superior and inferior petrosal Sinuses On the posterior inferior surface of the petrous part lies the jugular fossa Between the jugular fossa and the carotid canal is the tympanic Canaliculus The mastoid process extends posteriorly and has large mastoid air cell
Styloid process
Endochondral
A projection from the temporal boneThe stylomastoid foramen lies posterior to this process
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PARIETAL BONE
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PARIETAL BONE
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Characteristics
Parts Ossification Comments
Forms the majority ofthe cranial vaultProvides the attachment of the temporalis muscle. The four corners of the parietal are not ossified at birth and give rise to the fontanelles .There are 2 parietal bones.
Has 4 angles: ●Frontal— located at bregma● Sphenoid—located at pterion ● Occipital—, located at the lambda● Mastoid—located atasterion
Intramembranous
Relatively square, forming the roof and sides of cranial vaultEndocranial surface is filledwith grooves made by middle meningeal arterySigmoid sulcus is a groovecaused by the beginning of the transverse sinus located at mastoid angle
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SUTURAL / WORMIAN BONES Additional ossificatory
centres may occur in or near sutures, giving rise to isolated sutural bones.
Usually irregular in size and shape, and most frequent in the lambdoid suture, they sometimes occur at fontanelles, especially the posterior.
An isolated bone at the lambda is sometimes seen called the Inca bone or Goethe's ossicle.
Seen in great number in hydrocephallic skulls.
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SURFACE ANATOMY
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CHILD V/S ADULT SKULL
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AGE DETERMINATION Development of the nasal spine (by year 3) Completion of the hypoglossal canal (by
year 4) Formation of the foramen of Huschke (by
year 5), Ossification of the dorsum sellae (by year
5) Fusion of the different parts of the occipital
bone (by year 7). The fontanelles are usually all closed by
the middle of the second year.
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AGE DETERMINATION The posterolateral is the first to close in
the first two months after birth, and the anterior fontanelle is the last to close around the middle of the second year
The mastoid process appears in the second year and the metopic suture between the two frontal bones will close by year 4.
The spheno-occipital synchondrosis will fuse between 11 and 16 years in the female and 13 and 18 years in the male
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AGE DETERMINATION The vomer and the ethmoid will fuse
between 20 and 30 years of age. The last part of the skull to show active age-
related growth is the jugular growth plate, a small triangular area sited posterolateral to the jugular foramen in the occipitotemporal suture.
Fusion here does not begin until 22 years of age, and bilateral fusion may not be completed before 34 years
In a small proportion of individuals, the plate may remain unfused beyond 50 years
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SEXUAL VARIATIONMALE-
Robust Chin is more square Gonial angle less than 125 Condyles are larger More rounded and thick orbital margins The adult male cranium has 11% larger
cranial capacity than females, The male cranium tends to have thicker
bones. The muscle origins and insertions more
marked , e.g. the temporal and nuchal lines
The frontal sinuses are larger, as are the glabella and the superciliary arches
The external occipital protuberance and the mastoid processes are more prominent
Well defined glabella
FEMALE-
Gracile
Forehead – higher, Vertical , rounded than male
Retention of frontal eminence
Diagnosis of sex is most accurately assessed using multivariate statistical techniques such as discriminant function analysis.
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GEOGRAPHIC VARIATION African cranium are broader, with taller
upper faces, more inferiorly positioned nasal regions, and more prognathic mandibular and maxillary arches than crania from other parts of the globe.
European skulls tend to be narrow. They share many cranial similarities with American Indians
Asian skulls are typically wide (brachycephalic)
Australian are often characterized by narrow skulls (dolichocephaly)
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CONGENITAL ANOMALIES AFFECTING THE SKULL
Hemifacial microsomia (Goldenhar syndrome)-
The mastoid process shows degrees of hypoplasia.
Often there is frontal bossing. Ten percent of cases are bilateral, but
invariably one side is more severely affected.
Absence of the external auditory meatus is common.
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MANDIBULOFACIAL DYSOSTOSIS Teacher Collins syndrome Clinically the skull vault appears
normal, but on imaging it is seen that the supraorbital ridges are poorly developed.
Despite normal sutural development there may be increased digital markings on the inner table.
The mastoid processes are not pneumatized and may be sclerotic.
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CRANIOSYNOSTOSIS Occur as a result of small brain size or failure of
the development of fibrous bands between the sutures.
Metabolic disorders such as rickets and familial hypophosphatasia.
Raised intracranial pressure, visual deterioration and mental retardation may result.
Sagittal craniosynostosis occurs in conjunction with other sutures, e.g. Crouzon's syndrome.
Premature fusion of the coronal suture results in reduced anteroposterior development with marked supraorbital recession.
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Brachycephaly -- Short head
-- Coronal suture Scaphocephaly -- Keel-
shaped head -- Sagittal suture
Plagiocephaly -- Asymmetric head -- Unilateral coronal, Unilateral lambdoid
Trigonocephaly -- Triangular-shaped head -- Metopic suture
Acrocephaly -- Pointed head- Coronal/lambdoid suture
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Dolichocephaly -- Long head -- Sagittal
suture
Oxycephaly -- Tower-shaped head- Coronal / lambdoid or all sutures
Turricephaly -- Tower-shaped head -- Coronal suture
Kleeblattschädel -- Clover-leaf skull -- Multiple but not all sutures
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SYNDROMES ASSOCIATED- CROUZON'S, APERT Premature fusion of the coronal suture
characterizes cases of ACROCEPHALOSYNDACTYLY (APERT’S SYNDROME)
Early synostosis of the coronal ,sagittal, and lambdoid sutures occurs in craniofacial dysostosis (CROUZON’S SYNDROME)
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CONCLUSION
JUST AS THE CLINICIAN NEEDS THE MEDICAL
HISTORY TO MAKE A LOGICAL DIAGNOSIS,
SO TO THE ANATOMY IS ESSENTIAL FOR A
LOGICAL EXPLANATION OF ANY STRUCTURAL
AND FUNCTIONAL IMBALANCES IF IT DO
OCCURS
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REFERENCES 1. Churchill Livingstone - Gray's Anatomy–
Textbook of human anatomy - 40th Edition 2. F Netters -Head and Neck Anatomy for
Dentistry- 2nd edition. 3. McMinn’s -Color Atlas of Head and Neck
Anatomy- 3rd Edition. 4. James L. Hiatt, Leslie P. Gartner - Head and
Neck Anatomy- -4th edition. 5. Keith L. Moore- Clinically Oriented Anatomy-
6th Edition. 6. Geoffrey H. Sperber – Craniofacial
Development.
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THANK YOU FOR YOUR KIND ATTENTION AND ACTIVE PARTICIPATION
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Landmark Shape Location Pterion (G. wing) Junction of greater wing of sphenoid, squamous
temporal, frontal, and parietal bones; overlies course of anterior division of middle meningeal artery
Lambda (G. the letter L) Point on calvaria at junction of lambdoid and sagittal sutures
Bregma (G. forepart of head) Point on calvaria at junction of coronal and sagittal sutures
Vertex (L. whirl, whorl) Superior point of neurocranium, in middle with cranium oriented in anatomical (orbitomeatal or Frankfort) plane
Asterion (G. asterios, starry) Star shaped; located at junction of three sutures: parietomastoid, occipitomastoid, and lambdoid
Glabella (L. smooth, hairless) Smooth prominence; most marked in males; on frontal bones superior to root of nose; most anterior projecting part of forehead
Inion (G. back of head) Most prominent point of external occipital protuberance
Nasion (L. nose) Point on cranium where frontonasal and internasal sutures meet
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Foramina/Apertures Contents
Anterior cranial fossa Foramen cecum Nasal emissary vein (1% of population) Cribriform foramina in cribriform plate Axons of olfactory cells in olfactory epithelium that form
olfactory nerves Anterior and posterior ethmoidal foramina Vessels and nerves with same namesMiddle cranial fossa Optic canals Optic nerves (CN II) and ophthalmic arteries Superior orbital fissure Ophthalmic veins; ophthalmic nerve (CN V1); CN III, IV, and VI; and
sympathetic fibers Foramen rotundum Maxillary nerve (CN V2) Foramen ovale Mandibular nerve (CN V3) and accessory meningeal artery Foramen spinosum Middle meningeal artery and vein and meningeal branch of CN V3 Foramen laceruma Deep petrosal nerve and some meningeal arterial branches and small veins Groove or hiatus of greater petrosal nerve Greater petrosal nerve and petrosal branch of middle
meningeal arteryPosterior cranial fossa Foramen magnum Medulla and meninges, vertebral arteries, CN XI, dural veins, anterior and
posterior spinal arteries Jugular foramen CN IX, X, and XI; superior bulb of internal jugular vein; inferior petrosal and sigmoid
sinuses; and meningeal branches of ascending pharyngeal and occipital arteries Hypoglossal canal Hypoglossal nerve (CN XII) Condylar canal Emissary vein that passes from sigmoid sinus to vertebral veins in neck Mastoid foramen Mastoid emissary vein from sigmoid sinus and meningeal branch of occipital
artery artery The internal carotid artery and its accompanying sympathetic and venous plexuses actually pass horizontally across (rather than vertically through) the area of the foramen lacerum, an artifact of dry crania, which is closed by cartilage in life.
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