1. 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 Chondrocranium Postcranial Cranial Axial SplanchnocraniumDermatocranium Appedicular Vertebrae NotochordLimbs Girdles

2. The Axial Skeleton Vertebral column: Basic anatomy consists of… *Supporting body (centrum) *Neural arch (along with ligaments forms vertebral canal) *Processes (diapophyses, zygopophyses)

3. Atlas Axis Cervical Thoracic Lumbar Sacral Coccyx How can you tell one type of vertebrae from another? What function determines each form? The Axial Skeleton

4. Vertebral column morphogenesis: Mesenchymal cells surround notochord and neural tube Differentiate into chondroblasts Osteoblasts later deposit bone matrix on cartilage scaffolding (see Chpt. 7)

5. The Axial Skeleton Vertebral column of fish: Much diversity in the fossil record 2 basic zones of differentiation… Trunk (dorsals) Tail (caudals) Agnathans with lateral neural cartilages only On other fishes there is an elastic ligament connecting neural spines

6. The Axial Skeleton Development of tetrapod vertebrae: Different styles of centra resulted from fusing of intervertebral discs (intercentra) Amphicelous Opisthocelous Procelous Acelous Heterocelous

7. 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…

8. 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

9. 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?

10. 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