Dermal bone: Difference between revisions

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(I corrected some statements and added information.)
{{Unreferenced|date=December 2009}}
A '''dermal bone''' or '''membrane bone''' is a bony structure derived from [[intramembranous ossification]] forming components of the [[vertebrate]] [[skeleton]] including much of the [[skull]], [[jaw]]s, [[gill]]s covers, shoulder girdle and [[fin]]s spines and the [[exoskeletonshell]] (of [[tortoise]]s and [[turtle]]s). In contrast to [[endochondral ossification|endochondral]] bone, dermal bone does not form from cartilage that then calcifies, and it is often ornamented. Dermal bone is formed within the [[dermis]] and grows by accretion only – the outer portion of the bone is deposited by [[osteoblast]]s.
The function of some dermal bone is conserved throughout vertebrates, although there is variation in shape and in the number of bones in the [[skull roof]] and postcranial structures. In [[bony fish]], dermal bone is found in the fin [[Ray (fish fin anatomy)|rays]] and scales. Special examples of dermal bones include the [[clavicle]], [[patella]], and ''[[os cordis]]''.