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Axial Skeleton

Axial Skeleton. Skull Cephalization Neurocranium Protects brain & sensory structures Phylogeny – common to all vertebrates Replacement bone. Chondrocranium development. Prechordal cartilage (trabeculae cranii) form Underneath brain Anterior to notochord. Prechordal cartilage.

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Axial Skeleton

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  1. Axial Skeleton • Skull • Cephalization • Neurocranium • Protects brain & sensory structures • Phylogeny – common to all vertebrates • Replacement bone

  2. Chondrocranium development • Prechordal cartilage (trabeculae cranii) form • Underneath brain • Anterior to notochord

  3. Prechordal cartilage • Form under forebrain region • Form nasal = olfactory capsules • Form optic capsules in orbit • Form rostrum • Finally expands to become ethmoid plate

  4. Parachordal cartilage • Forms beside and posterior to notochord • Forms floor of hindbrain • Expands to form basal plate • Forms occipital condyles (1-2) and foramen magnum

  5. Sensory capsules • As floor of cranium forms, so do sensory capsules • Olfactory capsule • Otic capsule for inner ear structures • Optic capsule (not attached – outer covering of eyeball)

  6. Plate expansion • Ethmoid plate expands and unites with olfactory capsule • Basal plate expands and unites with otic capsule • Formina remain for nerves & blood vessels • Hypophyseal fenestra remains for pituitary gland

  7. Question • Singular of foramina? • Fenestra?

  8. Ossification Centers • Ethmoid plate, basal plate & sensory capsules ossify • Four ossification centers • Occipital (back), Otic (ear), Sphenoid (floor), Ethmoid (floor)

  9. Occipital Ossification Center • Foramen magnum • Basioccipital • Exoccipital • Supraoccipital • Occipital Condyles

  10. Otic ossification center

  11. Sphenoid ossification center • Basisphenoid • Presphenoid/Sphenethmoid

  12. Ethmoid ossification center • Ethmoid plate • Olfactory capsules • Turbinates in mammals

  13. Neurocranium • Look at Skull & Lower Jaw Components page

  14. Key Points • What is one important trend of the NEUROCRANIUM from the Skull & Lower Jaw Components page?

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