THE FACE. 147 



ternal extremity, under the interstice between the second small 

 and the first large molar tooth, is the anterior mental or maxil- 

 lary foramen, the termination of a large canal in either side of 

 the bone, and which conducts the inferior maxillary blood ves- 

 sels and nerve to the teeth. The foramen is directed obliquely 

 upwards and backwards, and transmits the remains of these 

 blood vessels and the nerve to the face. The chin is that part 

 of the bone between the anterior mental foramina. As the al- 

 veolar processes do not exist in early life, and in very advanced 

 age when the teeth are lost, the anterior mental foramen in 

 such cases is very near the superior margin of the bone. At 

 it an obtuse ridge of bone commences, and which ends in the 

 root or anterior edge of the coronoid process. The alveolar 

 processes of the last three molar teeth are placed within this 

 ridge, and project over the internal face of the bone. 



The internal or posterior face of the lower jaw is also marked 

 at the symphysis by a ridge passing from the superior to the in- 

 ferior margin. At the lower part of this ridge is a cleft pro- 

 cess, the posterior mental tubercle. Below this tubercle, on ei- 

 ther side, is a shallow fossa, for receiving the digastric muscle. 

 Between the lower margin of the bone and the protuberance 

 occasioned by the alveolar processes of the larger molar teeth, 

 is an oblong large fossa, made by the pressure of the sub-max- 

 illary gland. 



The alveolar processes form a semicircle, the extremities of 

 which are carried backwards with a slight divergence. The 

 parietes of the processes are thin, and present cutting edges. 

 They of course correspond, v in number and shape, with the roots 

 of the teeth which they have to accommodate. The anterior 

 ones are longer than the posterior. As a general rule, the alve- 

 olar processes may be said to come and depart with the teeth*, 

 but, when a single tooth is extracted, the alveolar cavity not 

 unfrequently is filled up with osseous matter, the edge of it alone 

 being removed. This occurs more frequently in the lower than 

 in the upper jaw. 



The base of the lower jaw does not present many marks 

 worthy of attention. It should be observed, that its anterior 

 part is thicker than the posterior; and that sometimes, just be- 



