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Axial Skeleton - Vertebrae
LocomotionProtects spinal cordSuspends trunk
Vertebrae
CentrumBody of vertebraSurrounds or replaces notochord
Centrum shape
Amphicelous (most fish, tailed amphibians)Opisthocelous (terrestrial salamanders, gar)Acelous (mammals)Procelous (reptiles, frogs)
Vertebrae
Vertebral archNeural archNeural spine = spinous processNeural canal = vertebral canal
Vertebrae
Hemal archChevron bone in amniotesVentral archway for caudal blood vesselsHemal spine
Vertebrae
Transverse processDiapophysis
Vertebrae
ZygaphophysesTetrapod featurePrezygapophyses – cranialPostzygapophyses - caudal
Development of vertebrae
AncientSclerotomes around notochordIntersegmental from the somitesCartilage replacement of notochordBone replacement of notochord
Vertebrae in advanced fish
Centrum replaces notochordDiplospondyly in tail
Vertebrae in fish
Regional differentiationDorsal = TrunkCaudal = tail
Vertebrae - fish
Craniovertebral jointNo movement
Vertebrae - Amphibians
Terrestrial lifeSpine must support bodyResists bending but provides mobility
Phylogeny of tetrapod vertebrae
Tetrapod centrum is the descendant of the Pleurocentrum, not the intercentrum
Vertebrae - amphibians
Zygapophyses
Vertebrae - amphibians
Regional differentiationCervical – usually oneTrunk = dorsal – ribs presentSacral – oneCaudal – no zygapophysesUrostyle – fused post-sacral vertebrae in
anurans
Skeletal support
Cervical vert.Cervical vert.
Trunk vert.with ribsTrunk vert.with ribs
Sacral vert.Sacral vert.
Caudal vert.Caudal vert.
Vertebrae - amphibians
Craniovertebral joint1-2 occipital condyles
Vertebrae - Reptiles
Centrum replaces notochordProcoelous centrumPleurocentrum is phylogenetic ancestral
centrum
Vertebrae - Reptiles
ZygapophysesNot in tail
Vertebrae - reptiles
Cervical – 8 including atlas and axisDorsals = Trunk (thoracic and lumbar)Sacral – 2 for stronger supportCaudal
– Chevron bone = hemal arch– Autonomy
Vertebrae - reptiles
Craniovertebral jointBall & socket type of jointSingle occipital condyle
Vertebrae - reptile
Atlas = C1Axis = C2
– Odontoid process for rotationProatlas in crocodiles anterior to atlas
Vertebrae - Birds
Centrum is heterocoelous
Vertebrae - birds
Numerous cervical vertebraeSingle occipital condyleTrunk = Thoracic vertebrae (tend to fuse)Synsacrum
– Last thoracic, all lumbar, 2 sacral, some caudalCaudal vertebrae
– Pygostyle supports tail feathers
Vertebrae - Mammals
Centrum is acelous 7 cervical Thoracics vary Lumbars vary Sacrum 3-5 Caudal
– Chevron bone– Coccyx
Vertebrae - Mammal
Intervertebral discFibrocartilagePulpy nucleus
Vertebrae - Mammal
Craniovertebral joint2 occipital condylesAtlasAxisFlex, extend, circle, rotate
Key Points – Evolutionary trend of vertebrae
Regional differentiation?Head/neck?Sacral stability?Zygapophyses?Loss of notochord?