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Skull and Visceral Skeleton

Skull and Visceral Skeleton. Skull: Neurocranium Dermatocranium Splanchnocranium: Palatoquadrate cartilage and replacement bone Meckel’s cartilage and replacement bone Skeleton of the branchial arches. Neurocranium. Primary braincase protects brain arises as cartilage, which...

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Skull and Visceral Skeleton

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  1. Skull and Visceral Skeleton Skull: • Neurocranium • Dermatocranium Splanchnocranium: • Palatoquadrate cartilage and replacement bone • Meckel’s cartilage and replacement bone • Skeleton of the branchial arches

  2. Neurocranium Primary braincase • protects brain • arises as cartilage, which... • is replaced by bone • similar development in all vertebrates

  3. Formation • Paired prechordal (neural crest) and parachordal (lat. plate mesoderm) cartilage. Also cartilage around olfactory, otic and, sometimes, optic capsules

  4. Parachordal cartilage unites to form basal plate and joins otic capsules • Prechordal cartilage unites to form ethmoid plate and joins olfactory (and optic) capsules

  5. Further development involves: • formation of walls • a cartilaginous tectum (lower vertebrates) • fenestra and foramina for passage of blood vessels

  6. Cartilaginous Neurocrania in Adult Vertebrates • Cyclostomes: individual components more or less independent throughout life • Cartilaginous fish: union of components to enclose brain forming the chondrocranium • Lower bony fish: cartilaginous neurocranium persists; overlain with dermal bone (chondrosteans and holosteans)

  7. Ossification Centers in Neurocranium • Occipital: 4 areas around the foramen magnum • Sphenoid: under midbrain and pituitary - forms sphenoid • Ethmoid: ethmoid plate and olfactory capsules. Tends to remain cartilaginous in adults as cribiform plate. • Otic: several bones form (prootics, opisthotic, epiotics form petrosal). Petrosal fuses with squamosal to form the temporal bone

  8. DermatocraniumMembrane bones of the skull which may have originated in bony dermal armor of the ostracoderms • In modern vertebrates, formation from subdermal mesenchyme of neural crest and lateral plate mesoderm rather than dermal mesenchyme • Basic structural elements: roofing bones of the neurocranium, marginal bones of upper jaw, bones of primary palate and opercular bones

  9. Roofing bones: nasal (N), frontal (F), parietals (P) and dermooccipitals (DO)

  10. Orbit of eye: lacrimal (lac), prefrontal (PF), postfrontal (PoF), postorbital (PO) and jugal.

  11. Posterior angle of skull: intertemporal (IT), supratemporal (ST), tabular (Tab), squamosal (Sq) and quadrojugal (Qj)

  12. Marginal bones of upper jaw: premaxillae (Pre) and maxilla

  13. Primary palatal bones: volmer (1), palatines (2), ectopterygoid (3), pterygoid (4) and parasphenoid (5)

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