INFERIOR MAXILLARY BONE. 



171 



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 which the Platysma Myoides is inserted. The 

 external oblique line and the internal or mylo-hyoidean line (to be afterwards 

 described), divide the body of the bone into a superior or alveolar, and an 

 inferior or basilar portion. 



The internal surface (Fig. 124) is concave from side to side, convex from 

 above downwards. In the middle line is an indistinct linear depression, cor- 

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



Fig. 124. Inferior Maxillary Bone. Inner Surface. Side Yicw. 



ENIO-HYO-GLOSSUS 



CCNIO-HYOiDEUS 



B o dy 



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 Glenio-hyoidei mus- 

 cles. 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 line (mylo-hyoidean) 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 portions, 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 mem- 

 brane of the mouth : whilst that below it presents an oblong depression, the 

 submaxillary fossa, wider behind than in front, for the lodgment of the sub- 

 maxillary 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 cavities are sixteen in number, arid vary in depth and size according to 

 the teeth which they contain. To its outer side, the Buccinator muscle is 

 attached as far forward as the first molar tooth. The inferior border is rounded, 



