axial skeleton - vertebrae locomotion protects spinal cord suspends trunk

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?