BIO 2310

Report
Axial Skeleton - Vertebrae

Locomotion
 Protects spinal cord
 Suspends trunk
Vertebrae

Centrum
 Body of vertebra
 Surrounds or replaces notochord
Centrum shape

Amphicelous (most fish, tailed amphibians)
 Opisthocelous (terrestrial salamanders, gar)
 Acelous (mammals)
 Procelous (reptiles, frogs)
Vertebrae

Vertebral arch
 Neural arch
 Neural spine = spinous process
 Neural canal = vertebral canal
Vertebrae

Hemal arch
 Chevron bone in amniotes
 Ventral archway for caudal blood vessels
 Hemal spine
Vertebrae

Transverse process
 Diapophysis
Vertebrae

Zygaphophyses
 Tetrapod feature
 Prezygapophyses – cranial
 Postzygapophyses - caudal
Development of vertebrae

Ancient
 Sclerotomes around notochord
 Intersegmental from the somites
 Cartilage replacement of notochord
 Bone replacement of notochord
Vertebrae in advanced fish

Centrum replaces notochord
 Diplospondyly in tail
Vertebrae in fish

Regional differentiation
 Dorsal = Trunk
 Caudal = tail
Vertebrae - fish

Craniovertebral joint
 No movement
Vertebrae - Amphibians

Terrestrial life
 Spine must support body
 Resists 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 differentiation
 Cervical – usually one
 Trunk = dorsal – ribs present
 Sacral – one
 Caudal – no zygapophyses
 Urostyle – fused post-sacral vertebrae in
anurans
Skeletal support
Cervical vert.
Trunk vert.
with ribs
Sacral vert.
Caudal vert.
Vertebrae - amphibians

Craniovertebral joint
 1-2 occipital condyles
Vertebrae - Reptiles

Centrum replaces notochord
 Procoelous centrum
 Pleurocentrum is phylogenetic ancestral
centrum
Vertebrae - Reptiles

Zygapophyses
 Not in tail
Vertebrae - reptiles
Cervical – 8 including atlas and axis
 Dorsals = Trunk (thoracic and lumbar)
 Sacral – 2 for stronger support
 Caudal

– Chevron bone = hemal arch
– Autonomy
Vertebrae - reptiles

Craniovertebral joint
 Ball & socket type of joint
 Single occipital condyle
Vertebrae - reptile

Atlas = C1
 Axis = C2
– Odontoid process for rotation

Proatlas in crocodiles anterior to atlas
Vertebrae - Birds

Centrum is heterocoelous
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
Vertebrae - Mammals






Centrum is acelous
7 cervical
Thoracics vary
Lumbars vary
Sacrum 3-5
Caudal
– Chevron bone
– Coccyx
Vertebrae - Mammal

Intervertebral disc
 Fibrocartilage
 Pulpy nucleus
Vertebrae - Mammal

Craniovertebral joint
 2 occipital condyles
 Atlas
 Axis
 Flex, extend, circle, rotate
Key Points – Evolutionary trend
of vertebrae

Regional differentiation?
 Head/neck?
 Sacral stability?
 Zygapophyses?
 Loss of notochord?

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