When active lies in Howship's lacuna - gives typical outline to surface of bone. Usually large and multi-nucleated. Mature bone formed by removal of first formed bone and its replacement by new bone - a process which goes on through life. Terms - primary and secondary bone, interstitial, compact or bundle, spongy cancellous and trabecular bone. Origin is first pharyngeal arch - mandibular arch and maxillary processes.
Arch comprises cartilage rod, artery, vein and nerve.
First bone of mandible seen in 6th week I.U. at bifurcation of inferior dental nerve at point of future mental foramen, lateral to Meckel's cartilage. Lateral and lingual plates formed to give trough con-taining developing tooth germs. Bone formation by intra-membranous ossification except later when condyler and coronoid processes are formed from secondary cartilage. Role of Meckel's cartilage is support and some incorporation into mandible in mid- line. Bone formed in halves uniting in first year after birth.