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The Skull and Visceral Skeleton

What is a skull? Morphologists may refer to… Neurocranium Dermatocranium Splanchnocranium We will consider the “skull” as the “skull” minus the jaws, which are derived from the splanchnocranium. The Skull and Visceral Skeleton.

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The Skull and Visceral Skeleton

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  1. What is a skull? Morphologists may refer to… Neurocranium Dermatocranium Splanchnocranium We will consider the “skull” as the “skull” minus the jaws, which are derived from the splanchnocranium The Skull and Visceral Skeleton

  2. Neurocranium (aka enodcranium, chondrocranium, primary braincase): * Protects the brain * Endochondral ossification The Skull and Visceral Skeleton

  3. The Skull and Visceral Skeleton Neurocranium origins: Mesenchyme from neural crest cells and mesoderm Cartilages… *Para and Pre-chordal *Otic, Olfactory, Optic “nose” “ears” and “eyes”

  4. Taxonomic variation of neurocrania: Agnatha… remain loosely associated, fibrous cover dorsally Cartilaginous fishes… highly developed, envelopes brain, NO bone Bony fishes… remains in primitive fish below dermatocranium, BUT teleosts and tetrapods exhibit endochondral ossification The Skull and Visceral Skeleton

  5. Neurocranial ossification centers: Occipital, Sphenoid, Ethmoid and Otic *Occipital 1-4 bones and one (reptiles, birds and early amphibians) or two (modern amphibians and mammals) occipital condyles What do these articulate with? The Skull and Visceral Skeleton

  6. Neurocranial ossification centers: *Sphenoid in humans is composite of neurocranium and palatoquadrate. Remains as separate bones in some species… rather than wings. Sella turcica part of this bone The Skull and Visceral Skeleton

  7. Neurocranial ossification centers: *Ethmoid has greatest tendencies to remain cartilage in tetrapods. Comprised of ethmoid plate and olfactory capsules In humans… *Interorbital *cribiform plate, cristi galli, conchae, and nasal cartilages The Skull and Visceral Skeleton http://www.theodora.com/anatomy/images/image153.gif

  8. Neurocranial ossification centers: *Otic bones surrounding the membranous labyrinth can fuse with occipitals or squamous (as in humans) to form the temporal bone The Skull and Visceral Skeleton http://embryology.med.unsw.edu.au/wwwhuman/Hum12wk/Hum12wk.htm#12weekHead

  9. Dermatocranium Derived from dermal bone… however, modern tetrapods exhibit mesenchyme migration and subdermal development 4 basic structures… The Skull and Visceral Skeleton 1) Above/alongside brain, 2) upper jaw margin, 3) primary palate and 4) opercular bones

  10. Dermatocranium: Palatoquadrate (cartilaginous fishes) is replaced by maxilla and premaxilla that fuses with other dermatocranial elements Vomer(s), palatines and pterygoids part of primary palate The Skull and Visceral Skeleton

  11. Dermatocranium: Operculars… bones that cover and protect the delicate gill structures of bony fish The Skull and Visceral Skeleton

  12. The Skull and Visceral Skeleton Amphibian skulls: Considerably modified from labyrinthodonts, but still platybasic Only apodans have fully ossified skull… Why? Columella ossified Otic capsule exposed dorsally and laterally and in anurans large spaces exist inferiorly too

  13. Non-avian reptile skulls: Stem reptiles similar to basal amphibians Modern reptiles still have some ancestral characteristics, namely well ossified neurocranium and single occipital condyle Parietal foramen (sphenodon and many saurians) Why? The Skull and Visceral Skeleton

  14. “Apsidity”: Stem reptiles lacked temporal fossae (An-apsid skull) Ancestors to mammals have a single fossae (syn-apsid skulls) Modern reptiles have two fossae (di-apsid skull) Extinct dinosaurs have single superior fossae (Eury-apsid skull) that may be convergent evolution The Skull and Visceral Skeleton

  15. Secondary palate: Development of secondary palate makes internal nares positioned caudad The Skull and Visceral Skeleton

  16. Cranial kinesis: Movement of various functional parts of the skull independent of other parts is cranial kinesis Teleost, squamates and birds well adept at this… for example fish can move maxillae and palate independent of the neurocranium The Skull and Visceral Skeleton Why?

  17. Birds: Modified reptile skull in 2 functional regions…1) brain box2) food getter Light weight dermal bones and bigger space for large brain The Skull and Visceral Skeleton

  18. Mammals: Key features are single dentary (mandible), modified secondary palate and 3 ossicles The Skull and Visceral Skeleton

  19. The Skull and Visceral Skeleton

  20. Visceral skull: Derived from pharyngeal arches… in fishes becomes the jaws and gill arches Origins are neural crest cells Meckel’s cartilage behind the palatoquadrate (jaw) is homologous to the ossicles in mammals. The Skull and Visceral Skeleton

  21. Articular cartilage becomes one of the 3 ossicles in mammals… The Skull and Visceral Skeleton

  22. Meckel’s cartilage becomes one of the 3 ossicles in mammals… The columella (or stapes) is present in basal groups. The Skull and Visceral Skeleton

  23. Other pharyngeal arches become portions of: 1) Styloid process2) Hyoid bone 3) Thyroid cartilage 4) Cricoid cartilage The Skull and Visceral Skeleton

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