Dermal bone

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A dermal bone or membrane bone is a bony structure derived from intramembranous ossification forming components of the vertebrate skeleton including the skull, jaws, gills, fins and exoskeleton (of tortoises and turtles). In contrast to endochondral bone, dermal bone does not form from cartilage that then calcifies. Dermal bone is formed within the dermis and grows by accretion only – the outer portion of the bone is deposited by osteoblasts.

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 rays and scales. Special examples of dermal bones include the clavicle, patella, and os cordis.