THE INFERIOR MAXILLARY BONE. 



59 



Above this are the mental spines, the lower being a small median ridge (often only a 

 slight roughness), to which the genio-hyoid muscles are attached, and the upper a 

 pair of more prominent tubercles, giving origin to the genio-glossi. Above the 

 upper spines a small median foramen penetrates the bone, and continued upwards 

 from this there is often to be seen a narrow groove marking the symphysis. Begin- 

 ning below the mental spines, and passing backwards and upwards to the ramus, is 

 the prominent internal oblique line or mylo-hyoid ridge, which gives origin to the 

 mylo-hyoid muscle, and at its hinder end to a slip of the superior constrictor of the 



EXT. OBL. LINE. 



PROTUBERANCE 



TUBERCLE 



Fig. 61. THE INFERIOR MAXILLARY BONE, FROM THE RIGHT SIDE. (Drawn by D. Gunn.) 



pharynx. Above this line is a smooth depression for the sublingual gland, and 

 more posteriorly beneath it another for the submaxillary gland. 



The ramus is thinner than the body of the bone. Its posterior border in meeting 

 the line of the base forms the angle of the jaw, which is more or less rounded off, 

 and usually a little everted. The external surface is flat and impressed by the 

 masseter ; towards the angle irregular oblique ridges mark the attachment of 

 tendinous bundles of the muscle. The internal surface presents about its middle, 

 and on a level with the crowns of the lower molar teeth, the inferior dental foramen, 

 leading into the dental canal, which lodges the dental nerve and vessels. The inner 

 margin of the foramen is sharp and prominent anteriorly, forming the lingula. 

 Beginning at a notch behind the lingula is the mylo-hyoid groove (occasionally a 

 canal for a short space), marking the passage of the mylo-hyoid nerve with com- 

 panion vessels : it runs downwards and forwards to the body of the bone, and 

 terminates below the hinder end of the mylo-hyoid ridge. Behind this, and reaching 

 down to the angle, is a marked roughness for the internal pterygoid muscle. 



The ramus is surmounted by two projections, the cTmdyle and the coronoid 

 process, which are separated by a deep excavation, the sigmoid notch. The condyle 

 is continued upwards from the posterior part of the ramus. It is supported by a 

 constricted portion, the necJc, on the front of which is a depression for the insertion 



