09 19 07 - Cranial Skeleton I

09 19 07 - Cranial Skeleton I - Chapter 7: The Cranial...

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Chapter 7: The Cranial Skeleton Two kinds of bone with regard to ontogeny. Dermal bones/intramembranous ossification – ossifies directly Forms in dermis Secrete matrix where they are Cells gather around outside of bone Endoskeletal bone/Replacement (endochrondral) bone - replaces cartilage (see pp.114-115 about cartilage) Form on top of a cartilage template Works as a place for bone to grow Cartilage forms first Then it gets replaced by bone Both types of bone are identical once formed--but origin and homologies of various bones can be established by knowing how a bone develops. Divisions of the skeleton Cranial skeleton Chondrocranium – lower braincase “cranial base” Supports base Visceral skeleton – (viscerocranium) pharyngeal arches “Splanchnocranium” Splanchno=visceral Dermatocranium – upper braincase “cranial vault” Dermal bones of skull Form in developing dermis of head Cover roof and side of head, not base Postcranial skeleton – everything below the head OR… Axial skeleton – skull, vertebrae, ribs, sternum, median fins (fish), spinal cord Appendicular skeleton – pectoral and pelvic girdles, forelimbs and hindlimbs I. Components of the skull A. Chondrocranium – formed from cartilage that may be replaced by bone Oldest portion of cranium Several origins: neural crest, somites, chordamesoderm Usually well fused, but elements distinct in embryo form from 5 groups of cartilages: Notochord- turns into part of base of brain basal plate-forms very bottom
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This note was uploaded on 08/16/2008 for the course BIOL 276 taught by Professor Johnson during the Spring '07 term at UNC.

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09 19 07 - Cranial Skeleton I - Chapter 7: The Cranial...

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