The Axial Skeleton

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The Axial Skeleton
Even craniates may have an exoskeleton and an
endoskeleton Which type is derived from dermis
and epidermis? Some bones have left their
original place to sink and fuse with other
bones. We will identify units and discuss their
origins Cranial and postcranial Axial and
appendicular
Skeleton
Postcranial
Cranial
Splanchnocranium
Dermatocranium
Chondrocranium
Axial
Appedicular
Vertebrae
Girdles
Notochord
Limbs
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The Axial Skeleton
Vertebral column Basic anatomy consists
of Supporting body (centrum) Neural arch
(along with ligaments forms vertebral
canal) Processes (diapophyses, zygopophyses)
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The Axial Skeleton
How can you tell one type of vertebrae from
another?
Atlas
Axis
Cervical
Thoracic
Lumbar
Sacral
Coccyx
What function determines each form?
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The Axial Skeleton
Vertebral column morphogenesis Mesenchymal cells
surround notochord and neural tube Differentiate
into chondroblasts Osteoblasts later deposit bone
matrix on cartilage scaffolding (see Chpt. 7)
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The Axial Skeleton
Vertebral column of fish Much diversity in the
fossil record 2 basic zones of differentiation Tr
unk (dorsals) Tail (caudals) Agnathans with
lateral neural cartilages only On other fishes
there is an elastic ligament connecting neural
spines
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The Axial Skeleton
Development of tetrapod vertebrae Different
styles of centra resulted from fusing of
intervertebral discs (intercentra) Amphicelous Opi
sthocelous Procelous Acelous Heterocelous
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The Axial Skeleton
Cervical vertebrae C1 C2 Odontoid process and
transverse alantal ligament Cervical vertebrae
vary among species Birds heterocelous and long
(25 in swans) Most all mammals have 7 vertebrae,
centra lengths differ
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The Axial Skeleton
Sacrum and synsacrum Modified by ankylosed ribs
and transverse spines Also often fused
(ankylosed) with adjacent vertebrae NOT with
tetrapods that lack hindlimbs 1- 13 Synsacrum
of birds and armadillos
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The Axial Skeleton
Ribs Ribs of tetrapods Homologous with dorsal
ribs of some fish species Often two articulating
surfaces or heads (bicipital) capitulum and
tuberculum Related to transverse foramina in
humans 2 parts costal rib and sternal rib How
about anurans and urodelans?
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The Axial Skeleton
Sternum Absent in many craniates Largely a
tetrapod structure however, crocodilians, turtles
and urodelans lack a sternum. In humans 3
parts Manubrium Body Xiphoid process