Intramembranous ossification is seen in whichbones?
Correct Answer: Maxilla
Description: Ans. is 'c' i.e., Maxilla Bone formation Bone formation (ossification) occurs by two methods : 1) Endochondral ossification, 2) Intramembranous ossification. In both, mesenchymal connective tissue is replaced by bone but by different mechanics. Endochondral ossification This type of ossification involves the replacement of a cailaginous model by bone. Bone formation takes place in pre-existing cailage. Mesenchymal tissue first forms cailage which is latter ossified to become bone. Most of the longs bones develop by endochondral ossification. Other bones are veebrae, pelvis, skull base bones. Interstitial growth of long bone at epiphyseal cailage occurs by endochondral ossification. Intramembranous ossification Mesenchymal cells give rise to osteogenic cells which develop into osteoblasts. steoblasts begin to lay down osteoid which latter mineralised to form bone Thus, there is direct formation of bone from mesenchymal tissue (with no cailage formation as occurs in Endochondral ossification). This type of ossification transforms membrane into bone. The bone formation occurs at the periphery with layers of bone being laid down analogous to the ring-like diameter of a tree. This type of growth is called appositional growth. Skull vault, maxilla, most of the mandible and clavicle are formed by intramembranous ossification.
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