INFERIOR MAXILLARY BONE. 93 



incisor teeth, is a depression, the incisive fossa, for the attachment of the Levator 

 menti ; and, still more externally, a foramen, the mental foramen, for the passage 

 of the mental nerve and artery. This foramen is placed just below the root of 

 the second bicuspid tooth. Running outwards from the base of the mental process 

 on each side, is a well-marked ridge, the external oblique line. This ridge is at 

 first nearly horizontal, but afterwards inclines upwards and backwards, and is 

 continuous with the anterior border of the ramus ; it affords attachment to the 

 Depressor labii inferioris and Depressor anguli oris; below these the Platysma 

 myoides is inserted. The external oblique line, and the internal oblique or 

 mylo-hyoidean line, to be hereafter described, divide the body of -the bone into 

 a superior or alveolar, and an inferior or basilar portion. 



Fig. 56. Inferior Maxillary Bone. Outer Surface. Side View. 



The internal surface (fig. 57) is concave from side to side, convex from above 

 downwards. In the middle line is an indistinct linear depression, corresponding 

 to the symphysis externally; on either side of this depression, just below its 

 centre, are four prominent tubercles, placed in pairs, two above and two below ; 

 they are called the genial tubercles, and afford attachment, the upper pair to the 

 Genio-hyoglossi muscles, the lower pair to the Grenio-hyoidei muscles. Sometimes 

 the tubercles on each side are blended into one, or they all unite into an irregular 

 eminence of bone, or nothing but an irregularity may be seen on the surface of 

 the bone at this part. On either side of the genial tubercles is an oval depression, 

 the sublingual fossa, for lodging the sublingual gland ; and beneath the fossa a 

 rough depression on each side, which gives attachment to the anterior belly of the 

 Digastric muscle. At the back part of the sublingual fossa, the internal oblique 

 or mylo-hyoidean line commences ; it is at first faintly marked, but becomes more 

 distinct as it passes upwards and outwards, and is especially prominent opposite 

 the last two molar teeth ; it divides the lateral surface of the bone into two por- 

 tions, and affords attachment throughout its whole extent to the Mylo-hyoid 

 muscle, the Superior constrictor being attached above its posterior extremity, 

 nearer the alveolar margin. The portion of bone above this ridge is smooth, and 

 covered by the mucous membrane of the mouth ; whilst that below it presents 

 an oblong depression, the submaxillary fossa, wider behind than in front, for the 

 lodgment of the submaxillary gland. The superior or alveolar border is wider, 

 and its margins thicker, behind than in front. It is hollowed into numerous 

 cavities, for the reception of the teeth ; these are sixteen in number, and vary in 

 depth and size according to the teeth which they contain. The inferior bonier is 

 rounded, longer than the superior, and thicker in front than behind ; it presents 



