396 



MAMMALIAN ANATOMY 



molar tooth had a minute additional fang, which was planted in a little 

 alveolus oil the outer side of the posterior fang. 



The variations in the anterior dental foramen have been already 

 pointed out (page 389). When the lower border of the bone is held 

 horizontally, the posterior border of the coronoid process may be 

 vertical, or it may incline backward, so that the tip, which in some 

 specimens is slightly hooked, extends beyond the condyle. 



The condyle varies in relative length and width ; the outer end is 

 often pointed. The upper surface of the angle frequently presents a 

 deep fossa which is distinct from the fossa under the condyle. 



HUMAN MANDIBLE. 



In man the adult lower jaw is a single bone ; the two halves 

 early coalesce at the median symphysis. As a single bone it may be 



described as consisting of a horseshoe- 

 shaped body, from each posterior end of 

 which rises an almost vertical ram us 

 (Fig. 313). 



The body is vertical at the median 

 symphysis ; instead of sloping downward 

 and backward, as in the cat, it is produced 

 forward to form a chin, or mental pro- 

 tuberance. Above the chin on the ex- 

 ternal surface is the incisive fossa for 

 the levator mentis muscle, and behind 

 this, on each side and on a level with the 

 second premolar tooth, is the mental fora- 

 men. The external oblique line extends from the mental protuber- 

 ance to the anterior border of the ramus ; it offers attachment for 

 the depressores labii inferior and anguli oris muscles. The buccinator 

 muscle is attached to the external surface near the superior border, and 

 the platysma myoides at the rounded inferior border. 



The internal surface of the body exhibits in front, at the lower 

 part of the symphysis, two pairs of tubercles, whereof the upper pair 

 is for the attachment of the genio-hyo-glossus muscle and the lower 

 pair for the attachment of the genio-hyoid muscle. The shallow space 

 on each side of these tubercles is called the sublingual fossa ; the 

 roughened depression below them is for the insertion of the digastric 



MANDIBLE. 



l.body; 2, ramus; 3, symphysis; 4, base; 

 5, angle; 6, mental foramen; 7, condyle; 

 8, coronoid process; 9, mandibular, or sig- 

 moid, notch ; 10, dental foramen : 11, alve- 

 olar process ; 12, incisor teeth ; 13, canine 

 tooth ; 14, prernolars ; 15, molars. 



