Skeletal System of VertebratesBotones, Maria Elena S. Gaba, Chinee Anne Marie C.Kiamzon, Kristelle Ann A. Ortilla, Zsazsa D.Pascual, Leah Mae S.

SKELETAL SYSTEM

Skeletal System Most important organ system in the study of

vertebrate morphology.

- Provides reliable information about the specific adaptations of vertebrates such as posture and locomotor adaptations

- Tells about other organ systems

- Due to its hardness and durability, skeleton becomes fossilized and the study of past vertebrate life is mostly based on fossils

Functions Give shape to the body and support its

weight Offers a system of levers that aid muscles

to produce contraction Protects soft parts such as nerves, blood

vessels and other viscera Two types of skeleton

Exoskeleton (protective structure on the outside of the body)

Endoskeleton (protective structure on the inside of the body)

Endoskeleton

Exoskeleton

Functions Two separate components

Cranial skeleton or the skull Postcranial skeleton (axial and

appendicular)

Composed of mineralized connective tissues ( dentin, enamel, cartilage and mostly bones)

-mesenchyme differentiated into scleroblasts which give rise to osteoblasts, odontoblasts, chondroblast

and ameloblast.

Cartilage- Forms an important part of the endoskeleton in all

vertebrates- Cartilage is avascular tissue, - Other types include the elastic cartilage in the external ear

and epiglottis, and fibrous cartilage in the intervertebral discs and attachment of tendons and ligaments.

- Cartilage is a tough, elastic, fibrous connective tissue found in various parts of the body, such as the joints, outer ear, and larynx. A major constituent of the embryonic and young vertebrate skeleton, it is converted largely to bone with maturation.

Bones Comprise most of the endoskeleton in

higher vertebrates

Contrary to cartilage, blood vessels and nerves are present in bony tissues passing through small Haversian canals.

Haversian canals are located in the bone tissue at the center of the compact bone through which blood vessels, nerve fibres and lymph vessels pass.

Bones

Organic component is primarily collagen, which gives bone great tensile strength

Inorganic components of bone comprise 60% of the dry weight

Functions: - Support and movement via attachments for soft tissue

and muscle - Protects vital organs- Major site for red marrow for production of blood cells- Plays a role in metabolism of minerals such as calcium

and phosphorus

Bones

2 basic structural types based on bone tissue

- Compact bone- Spongy bone or

cancellous bonePeriosteum – dense layer

of connective tissue that surrounds the bone

As to kind of bone tissue

Cranial SkeletonSkeletal framework

of the head (skull)3 embryonic

components:

1. Chondrocranium

2. Dermatocranium

3. Splanchnocranium

ChondrocraniumComposed of cartilage which contributes

to the base of the skull, includes the sense capsule and in most vertebrates, is replaced by bone

Primary brain caseSurrounds the brain and the special

sense organs

Chondrocranium Ossification Centers

Occipital centers - cartilage surrounding the foramen magnum may be replaced by as many as four bones: one basioccipital, two exoccipital, and one supraoccipital The six centers that we can see on diagram are: - Basioccipital bone; - Exoccipital bone (two centers); - Supraoccipital bone; - Interparietal bone (two centers).

Sphenoid centers from basisphenoid bone, presphenoid bone, and the side walls above basisphenoid and presphenoid form orbitosphenoid, pleurosphenoid and alisphenoid.

Ethmoid centers tend to remain cartilaginous and form cribiform plate of ethmoid and several ethmoturbinal bones

Otic centers – the cartilaginous otic capsule is replaced in lower vertebrates by several bones: prootic, opithotic, epiotic

Types of Skull Based on Fenestrae (Temporal Openings)

1. Anapsid skull

- The primitive skull, has no temporal fenestra,

possessed by turtles and other primitive reptiles.

2. Diapsid skull

- The diapsid skull has two temporal fenestrae,

possessed by most members of diapsida including

crocodiles, birds and lizards.

3. Euryapsid skull – this is a derived diapsid

skull where the lower temporal fenestra is lost

4. Synapsid skull – has one fenestra located in

a different place than the euryapsid skull

DermatocraniumComposed of dermal bones that overlie the

chondrocranium and splanchnocranium

Forms the sides and roof of the skull protecting the brain, it also forms most of the bony lining of the roof of the mouth and encases much of the splanchnocranium

Completes the protective cover of the brain and jaws

Parts of Dermatocranium

Modern fishes and amphibians have simple skull and the number of dermal bones present is reduced, some have tended to be lost or fused

In amniotes, dermal bones predominate, forming most of the braincase and lower jaw; they are divided into six series of bones.

Parts of Dermatocranium

1. Facial Series – encircles the external naris forming the snout.

2. Orbital series – encircles the eye defining the orbit

3. Temporal series – lies behind the orbit completing the posterior wall of the braincase

4. Vault series or roofing bones – located across the top of skull covering the brain beneath

5. Palatal series – dermal bones of the primary palate covering the roof of the mouth

6. Mandibular series – encases the Meckel’s cartilage

Splanchnocranium

An ancient chordate structure associated with the filter feeding surfaces

Arises from the neural crest cells departed from the sides of the neural tube and migrate into the walls of the pharynx between successive pharyngeal slits

1. Meckel's Cartilage2. Palatoquadrate3. Rostrum4. Labial Cartilage 5. Basihyal Cartilage 6. Ceratohyal Cartilage 7. Hyomandibular Cartilage 8. Ceratobranchial Cartilage 9. Basibranchial Cartilage 10. Hypobranchial Cartilage 11. A. Mandibular Arch 12. B. Hyoid Arch 13. C. Branchial Arch Figure 2. Articulated chondrocranium and splanchnocranium

Types of Jaw Attachments1. Paleostylic – characteristic of Agnathans

- None of the arches attach directly to the skull

2. Euautostylic – the earliest jawed condition

- Found in Placoderms and Acanthodians

- The mandibular arch is suspended from the skull by itself without aid from the hyoid arch

3. Amphistylic – found in early sharks, some osteichthyians and crossopterygians

- Attached to the braincase through two primary articulations

- Anteriorly by a ligament connecting the palatoquadrate to the skull

- Posteriorly by the hyomandubula

4. Hyostylic – found in most modern bony fishes

- The mandibular arch is attached to the braincase primarily through the hyomandibula with the aid of the sympletic bone

5. Metautostylic – found in most amphibians, reptiles and birds.

- Attached to the braincase directly through the quadrate bone

- Formed in the posterior part of the palatoquadrate

6. Craniostylic – found in mammals

- The entire upper jaw is a part of the braincase but the lower jaw called dentary bone is suspended from the dermal squamosal bone of the braincase

- The palatoquadrate and Meckel’s cartilages remain cartilaginous exceot at their posterior ends which becomes the incus and malleus of the middle ear respectively

Postcranial SkeletonAxialAppendicularFunction of body skeleton includes- Protects the viscera- Contributes to ventilation of the lungs- Store for various minerals- Provides rigidity to the body- Provides series of firm and hinged segments needed for

locomotion in conjunction with the muscles

Axial Skeleton

Forms the main axis of the bodyComposed of the notochord, vertebral column, ribs, sternum and skull

Notochord The primitive axial skeleton,

replaced by the vertebral column

Unsegmented and composed of dense fibrous connective tissue

The first skeletal element to appear in the embryo of chordates

Structure and Development of Vertebral Column

The vertebral column is the

main axial support of vertebrates

A vertebra is composed of a

centrum, one or two arches, and

various processes

It protects the spinal cord and

provides rigidity to the body

Types of Vertebra Based on Centra

1. Aspondyly – no centra

2. Monospondyly – with only one centrum per segment

- Stereospondyly – a monospondylous vertebra in which the single centrum (intercentrum) is separate

3. Diplospondyly – with two centra per segment

- Embolomerous – a diplospondylous vertebra in which the approximate equal-sized centra are separate

No centra

4. Polyspondyly – with five to six centra per segment

5. Aspidospondyly – the centra and spines are separate

- Rhachitomous – an aspidospondylous vertebra with numerous separate parts that constitute each vertebral segment

6. Holospondyly – the centra and spines are fused into a single bone

-Lepospondyly - a holospondylous vertebra with a husk-shaped centrum usually pierced by a

notochordal canal.

Figure 2.33. Comparison of vertebrae of primitive tetrapods and modern amniotes. The rachitomous type (shown also in cross section, X.S.) occurred in crossopterygians and in the earliest amphibians. B is from a labyrinthodont in the reptile line. B1 and B2 are from other labyrinthodonts. Whether the modern amphibian centrum represents a hypocentrum (diagonal lines) or a pleurocentrum (stippled) is not certain. The unmarked part of the vertebra is the neural arch. Adapted, with permission, from Kent, G. C. 4th ed. Comparative anatomy of the vertebrates. St. Louis: C. V. Mosby Co.; 1978. [134]

Types of Centra Based on Shapes

1. Amphicoelous

2. Procoelous

3. Opisthocoelous

4. Heterocoelous

5. Acoelous

Structure and Function of Ribs

Series of cartilaginous or elongated bony structures served as attachment for the vertebrae extending into the body wall

- Provide sites for secure muscle attachment and help suspend the body

- Form a protective case (rib cage) around viscera

- In Amniotes, contributes to the breathing mechanism

Types of Ribs1. True ribs – meet ventrally with the

sternum, consist of two jointed segments

Vertebral or costal rib (proximal segment)

Sternal rib (distal segment)

Joint between costal and sternal ribs allows changes in chest shape during respiration

2. False ribs – articulate with each other but not with the sternum

3. Floating ribs – do not articulate ventrally

Structure and Function of Sternum A midventral skeletal element that usually articulates with the more anterior

thoracic ribs and with the pectoral girdle

Strictly a tetrapod structure and primarily, and amniote characteristic

- Strengthen the anterior part of the trunk and body wall

- Helps protect the thoracic viscera

- Accommodates muscles of the pectoral limbs

- In amniotes, helps in ventilating the lungs

The sternum forms either paired or midventral primodia that are regarded as new structures not derived from the pectoral girdle or ribs

Appendicular Skeleton

Structure and Evolution of Median Fins

Occur in all jawless vertebrates and fishes: Dorsal fins - located along the

middorsal line.Anal fins - located between anus and

tailCaudal Fin

DORSAL and ANAL FINS

o Prevent the body from turning around the vertical axis (yawing) and around the longitudinal axis (rolling).

o In primitive vertebrates, each fin is supported within the contour of the body by a series of rod-like radials or pterygiophores.

o The exposed membrane of fins of CEPHALASPIDS and some PLACODERMS are supported only by dorsal scales.

CAUDAL FINClassified into four types depending on size and shape of the spine.

1. Diphycercal – if the spine is straight to the tip of the tail with equal dorsal and ventral lobe of the tail. (ex. Cyclostomes, pleuracanths, and some sarcopterygians)

2. Hypocercal – if the spine tilts downward with longer ventral lobe than dorsal lobe.(ex.anaspids)

3. Heterocercal – if the spine tilts upward with longer dorsal lobe than ventral lobe.(ex.cephalaspids, placoderms, most chondrichthyes, and primitive osteichthyes)

4. Homocercal - if all the fin membrane is posterior to the spine with equal dorsal and ventral lobe.(ex.all teleosts)

Structures and Evolution of Girdles

Girdles of fisheso the pectoral girdle is older, larger and more complicated

than pelvic girdle.

-It includes one or more cartilage or replacement bones and several dermal bones derived from ancestral scales and armour plates.

o Placoderms cartilaginous fins was related to overlying plates of dermal skeleton.

o Cartiliginous fishes has no dermal elements

Scapulocoracoid – the right and left halves fused in the midline forming a U-shaped girdle

1.Ceratotrichia 2. Scapulocoracoid Bar3. Propterygium 4. Mesopterygium5. Metapterygium

A. Basal Pterygiophores

Girdle and Tetrapod

o BIRDS have a bladelike scapula that is oriented parallel to the spine.

- with large anterior coracoid that is articulated with the sternum

- the posterior coracoid has been lost

- two clavicles fuse ventrally forming the furcula or absent in some birds.

Girdle and Tetrapod

o the only membrane bone retained Therian Mammals is the clavicle

- The anterior coracoid is completely lost.

- the posterior coracoid fuses to the scapula forming the coracoid process of the scapula

- the scapula is unique in having spine which represents its anterior border

- the ventral end of the spine is continued as the acromion process to articulate with the clavicle.

Girdle and Tetrapod

o the pelvic girdle of Tetrapods is much enlarged over that of fishes and is relatively uniform in basic structure.

-each half of the pelvic girdle is a single cartilaginous unit in the embryo.

-three bones are constant in the adult:

a dorsal ilium, which articulates with one or more sacral vertebrae

an anterior pubis

A posterior ischium

-the bones of one side usually fuse in the adult forming the innominate bone

-one or both of the ventral bones of the two sides usually articulates of fuse across the midventral line, the contact is called pelvic symphysis

Girdle and tetrapod

Primitive amphibians had a solid, triangular shaped pelvic girdle with the ilium forming the apex

- the pubis can be distinguished from the ischium by having a obturator foramen that accommodates a nerve.

In FROG, the girdle has a long, anteriorly inclined ilium and cartilaginous pubis.

Girdle and Tetrapod

REPTILES has various shapes patterned after the basic plan of LABYRINTHODONTS

-the contact with the spine is firmer

-the large pubo-ischiadic fenestrum is present between the two ventral bones

Birds have a large pelvic girdle that is firmly attached to the synsacrum

-the long ilium extends both anterior and posterior to the socket for the femur or acetabulum: The pubis is turned backward below the ischium and there is no symphysis

Girdle and Tetrapod Mammals have a long and expanded ilium

extending only forward from the acetabulum

- the large obturator fenestrum represents both the obturator foramen and the pbo-isichiadic fenestrum of the ancestor.

- a symphysis is always present

- MONOTREMES and MARSUPIALS have epipubic bones that articulate with the pubic bones extending forward in the ventral body wall.

MISCELLANEOUS BONES

SESAMOID BONE – bones embedded in or interrupting tendon

the largest is patella or knee cap

Baculum (os penis) – bone in the penis of carnivores, bats, insectivores, rodents, and some primates

Additional small bones are found in the different structures among TETRAPODS:

in the eyelids of CROCODILIANS

in the crest of a BIRD

in the snout of PIGS

at the base of the external ear of some RODENTSBaculum of a dog’s penis

TYPES of LOCOMOTION IN MAMMALS

posterior limbs provide rapid acceleration and often support the greater part of the weight.

Types of locomotion

used by Tetrapods:

- GRAVIPORTAL

- CURSORIAL

- VOLANT

- AERIAL

- SALTATORIAL

TYPES of LOCOMOTION in MAMMALS

- AQUATIC

- FOSSORIAL

- SCANSORIAL

- ARBOREAL

Comparison of Vertebrates

Vertebrates Type of Skull Type of Jaw Attachment

Fishes Euryapsid Paleostylic/Hyostylic/ Amphistylic

Amphibians Anapsid Metautostylic

Reptiles Anapsid Metautostylic

Birds Diapsid Metautostylic

Mammals Synapsid Craniostylic

Type of Skull and Jaw Attachment

Girdles and Fins/Limbs

Dorsal and Caudal

Short/long bones

Hindlimbs are larger than forelimbs

Slightly broader and segmented

Uniform and specialized limb structure

Centra and Vertebral ColumnVertebrates Types of Centra based on

shapeRegions of Vertebral Column

Fishes Amphicoelus Anterior and Posterior (2)

Amphibians Amphicoelus, Procoelus or Opisthocoelous

there is little or no regional specialization of the vertebral column

Reptiles Procoelus 4 or 5 distinct region

Birds Heterocoelus consists of vertebrae, and is divided into three sections: cervical (11-25) (neck),

Synsacrum (fused vertebrae of the back, also fused to the hips (pelvis)), and

pygostyle (tail).

Mammals Acocoelus 5 distinct regions: Cervical, Thoracic, Lumbar, Sacral and Caudal

Trunk and tail

Ribs and SternumVertebrates Ribs Sternum

Fishes Dorsal and ventral set Absent

Amphibians Dorsal andventral set Some(In early amphibians it is absent

xiphisternum; Anurans omosternum)

Reptiles Cervical ribs Some

Birds Uncinate processes (are extensions of bone that project

caudally from the vertical segment of each rib)

Present(Large:Carina)

Mammals only have distinct ribs on the thoracic vertebra, although fixed cervical ribs are also present in monotremes

Present(sternebrae: modified into

manubrium and xiphisternum)

Most do not have ribs

Flight muscle

Girdles and Fins/Limbs

Vertebrates Girdles Fins/Limbs

Cartilaginous Fishes Large pectoral girdle Fins

Bony Fishes Increased girdle Fins

Amphibians Long girdle Limbs

Reptiles Various shapes Limbs

Birds Large pelvic girdle Limbs

Mammals Long and expanded Limbs