axial skeleton skull cephalization neurocranium – protects brain & sensory structures –...
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Axial Skeleton
SkullCephalizationNeurocranium
– Protects brain & sensory structures– Phylogeny – common to all vertebrates– Replacement bone
Chondrocranium development
Prechordal cartilage (trabeculae cranii) form
Underneath brainAnterior to notochord
Prechordal cartilage
Form under forebrain regionForm nasal = olfactory capsulesForm optic capsules in orbitForm rostrumFinally expands to become ethmoid plate
Parachordal cartilage
Forms beside and posterior to notochordForms floor of hindbrainExpands to form basal plateForms occipital condyles (1-2) and foramen
magnum
Sensory capsules
As floor of cranium forms, so do sensory capsules
Olfactory capsuleOtic capsule for inner ear structuresOptic capsule (not attached – outer covering
of eyeball)
Plate expansion
Ethmoid plate expands and unites with olfactory capsule
Basal plate expands and unites with otic capsule
Formina remain for nerves & blood vesselsHypophyseal fenestra remains for pituitary
gland
Ossification Centers
Ethmoid plate, basal plate & sensory capsules ossify
Four ossification centersOccipital (back), Otic (ear), Sphenoid
(floor), Ethmoid (floor)
Occipital Ossification Center
Foramen magnumBasioccipitalExoccipitalSupraoccipitalOccipital Condyles