OSTEOLOGY. 41 



Superiorly it is covered by tlie gums ; below tliis depressor 

 labii inferioris lias its origin. The external margin presents 

 three alveolar cavities for the lower incisors, slightly 

 smaller than those in the upper jaw, and behind these, 

 after a short interval, the alveolar cavitij for the tush, which 

 is more anteriorly placed than its superior corresponding 

 cavity. The internal "mar gin is rough, and by uniting 

 with its fellow forms the symphysis. Behind the body 

 the bone is constricted, forming the neck, which partly lies 

 in contact with the buccal mucous membrane. Its external 

 surface superiorly presents the curved line of attachment 

 of carinus ; below this is the anterior maxillary foramen or 

 foramen menti. Below this the bone is subcutaneous. 

 Both its superior and its inferior margins are rounded. 

 The latter to its inner side has digastricus attached as far 

 forward as the symphysis. The neck terminates posteriorly 

 where the alveolar cavities of the molars commence. They 

 resemble iu general cliaracters and number those of the 

 upper jaw, and occupy a considerable portion of the superior 

 margin of the bone, which extends gradually backwards 

 and upwards, and which from the last alveolar cavity 

 curves upwards to join the anterior margin of the coracoid 

 process, aifording attachment to buccinator and to re- 

 tractor labii inferioris. Buccinator also becomes attached 

 to the bone up against the alveolar cavities on the external 

 surface ; below this retractor labii inferioris runs forwards, 

 the rest of the anterior part of this surface is separated from 

 the skin only by retractor anguli oris. But behind the 

 molars the bone becomes much expanded, in consequence 

 of increased convexity of the inferior margin, which pro- 

 trudes postero-inferiorly forming the angle of the jaw to 

 which sterno-and stylo-maxillaris are attached, the latter 

 to the inner, the former to the outer edge. The margin 

 above this is thickened and tuberous. The parotid gland 

 is in contact with it. The expanded portion is termed the 

 ramus or branch, and being concave both externally and 

 internally its central portion is very thin. On both sur- 

 faces it presents roughened ridges extending from above 

 downwards which on the external surface serve to give 

 attachment to masseter externus, on the inner side to 

 masseter internus, which latter muscle hides the posterior 

 maxillary foramen to which the inferior dental artery and 

 nerve pass, and having entered it course along below the 



