1. Axial skeleton

2.  Encloses spinal cord, (dorsal aorta)  Site of muscle attachment  Suspends body - tetrapods

3. Somites Somites – metameric blocks of mesoderm that form early in development Somites in green

4. Somites –  Dermatome  Sclerotome  Myotome

5.  Neural (Vertebral)arch  Hemal arch  Neural, hemal spines Vertebral structure

6. Most vertebrates have centra that unite with arches

7. Shapes of the Centrum

8. Pad of notochord bw vertebrae  compression and bulging  dislocation Amphicoelous

9. Articulate in ball and socket fashion  Intervertebral pad is ossified  Nerve cord bending Opisthocoelous, Procoelous

10. Titanoboa

11. Centra are flattened – distributes compression equally  Intervertebral disks, notochord Acoelous

12. Interlocking ‘saddle’ shapes  Twisting prevented, yet flexible Heterocoelous

13. Vertebral development

14.  Dorsal ribs, ventral ribs Ribs and sternum

15.  Diapophysis, parapophysis Ribs and sternum

16. Ribs meet ventrally at sternum for many tetrapods (mostly amniotes)  Lung ventilation Amphibian Amniote Ribs and sternum

17. True ribs False ribs Floating rib Ribs and sternum

18.  Change from water to land... Evolution of the axial skeleton

19.  Lateral forces, compression, dislocation  Extended neural, hemal arches  Trunk vs. tail vertebrae Fish

20.  Land not level - need dorsal-ventral flexion Tetrapod forces

21.  Land not level - need dorsal-ventral flexion  Lateral flexion for some vertebrates Tetrapod forces

22. Vertebrae experience torsion forces Tetrapod forces

23. Tetrapods – resists torsion forces Zygapophyses Prezyg. Postzyg.

24. Fish vs. tetrapods: regionalization

25. Amphibian regionalization

26. 1: Atlas - ringlike 2: Axis - odontoid process extends forward into atlas Amniote cervical region No zygopophyses human dog

27. Changes to regionalization Amniotes have atlas, axis and other cervical

28. Cervical, thoracic, lumbar, sacral, caudal  Lumbar vs. thoracic Mammal regionalization

29. Comparing relative lengths of lumbar area

30. Comparing length and broadness of neural spines

31.  Cervical vertebrae  Zygapophyses  Hemal arch Modifying tetrapods to be aquatic

32. Turtle rib modification

33. Bird axial modifications

34. Keel of sternum Uncinate process Synsacrum Tradeoff of strength and flexibility