1. Axial Skeleton - Vertebrae Locomotion Protects spinal cord Suspends trunk

4. Vertebrae Centrum Body of vertebra Surrounds or replaces notochord

6. Centrum shape Amphicelous (most fish, tailed amphibians) Opisthocelous (terrestrial salamanders, gar) Acelous (mammals) Procelous (reptiles, frogs)

8. Vertebrae Vertebral arch Neural arch Neural spine = spinous process Neural canal = vertebral canal

10. Vertebrae Hemal arch Chevron bone in amniotes Ventral archway for caudal blood vessels Hemal spine

13. Vertebrae Transverse process Diapophysis

15. Vertebrae Zygaphophyses Tetrapod feature Prezygapophyses – cranial Postzygapophyses - caudal

17. Development of vertebrae Ancient Sclerotomes around notochord Intersegmental from the somites Cartilage replacement of notochord Bone replacement of notochord

20. Vertebrae in advanced fish Centrum replaces notochord Diplospondyly in tail

21. Vertebrae in fish Regional differentiation Dorsal = Trunk Caudal = tail

23. Vertebrae - fish Craniovertebral joint No movement

24. Vertebrae - Amphibians Terrestrial life Spine must support body Resists bending but provides mobility

26. Phylogeny of tetrapod vertebrae Tetrapod centrum is the descendant of the Pleurocentrum, not the intercentrum

28. Vertebrae - amphibians Zygapophyses

29. Vertebrae - amphibians Regional differentiation Cervical – usually one Trunk = dorsal – ribs present Sacral – one Caudal – no zygapophyses Urostyle – fused post-sacral vertebrae in anurans

30. Skeletal support Cervical vert. Trunk vert. with ribs Trunk vert. with ribs Sacral vert. Caudal vert.

32. Vertebrae - amphibians Craniovertebral joint 1-2 occipital condyles

33. Vertebrae - Reptiles Centrum replaces notochord Procoelous centrum Pleurocentrum is phylogenetic ancestral centrum

34. Vertebrae - Reptiles Zygapophyses Not in tail

35. Vertebrae - reptiles Cervical – 8 including atlas and axis Dorsals = Trunk (thoracic and lumbar) Sacral – 2 for stronger support Caudal – Chevron bone = hemal arch – Autonomy

38. Vertebrae - reptiles Craniovertebral joint Ball & socket type of joint Single occipital condyle

40. Vertebrae - reptile Atlas = C1 Axis = C2 – Odontoid process for rotation Proatlas in crocodiles anterior to atlas

42. Vertebrae - Birds Centrum is heterocoelous

44. Vertebrae - birds Numerous cervical vertebrae Single occipital condyle Trunk = Thoracic vertebrae (tend to fuse) Synsacrum – Last thoracic, all lumbar, 2 sacral, some caudal Caudal vertebrae – Pygostyle supports tail feathers

47. Vertebrae - Mammals Centrum is acelous 7 cervical Thoracics vary Lumbars vary Sacrum 3-5 Caudal – Chevron bone – Coccyx

53. Vertebrae - Mammal Intervertebral disc Fibrocartilage Pulpy nucleus

55. Vertebrae - Mammal Craniovertebral joint 2 occipital condyles Atlas Axis Flex, extend, circle, rotate

57. Key Points – Evolutionary trend of vertebrae Regional differentiation? Head/neck? Sacral stability? Zygapophyses? Loss of notochord?