254 



Anatomy of Skeleton 



physis. Each half has a ramus and a body, joined at an angle that varies with age and 

 dentition. The term angle of the jaw, however, is applied to the prominence formed by 

 the junction of the lower border of the body with the back margin of the ramus. 



The ramus ends above in two processes the coronoid process in front and the 

 articular head behind, supported by the narrower neck. The two processes are separated 

 by the coronoid or sigmoid notch . The front margin of the ramus is sharp, whereas the 

 posterior margin is blunt and rounded. The outer surface is roughened by the insertion 

 of the Masseter. On the inner side it presents (Fig. 202) the inferior dental foramen, ' \\ 

 whose inner lip is prolonged forward and upward into the lingula : leading downward 

 and forward from the foramen toward the body is the mylo-hyoid groove. A rough area 

 below and behind the foramen marks the insertion of the Internal Pterygoid. 



The body has a thick rounded lower part or splenium supporting the alveolar portion, 

 which contains the teeth. On the inner side is the continuation of the mylo-hyoid groove, 



eoronoi.A 



and above this the mylo-hyoid 



md 



'ike, 



Alvtoliis 

 Symph. 



Jplenium 



Mrttal 

 4ONTIMI, 



FIG. 01. Mandible from the front and right side. 



riUge or internal oblique line, 

 for attachment of Mylo- 

 hyoid (Fig. 202). 



' Below the back part of 

 these is the submaxillary 

 fossa, and above their front 

 part is the sublingual fossa : 

 these are in relation with the 

 corresponding glands. In 

 front of the submaxillary 

 fossa, and below the front 

 part of the mylo-hyoid ridge, 

 is a digastric depression or 

 fossa for anterior belly of 

 Digastric, which may, how- 

 ever, present itself in the 

 form of a slightly elevated 

 roughness. The mylo-hyoid 

 line on each side nearly reaches the symphysis, and, above its level and on each side 

 of the symphysis, are the genial tubercles for Genio-hyoids and Genio-glossi : these 

 are described as forming two pairs, upper and lower, but usually it is difficult to 

 distinguish them in this way, and there may be four tubercles, or a pair of them, or 

 a vertical ridge representing them more or less fused. 



On its outer aspect the body presents, from before backward, the vertical ridge of 

 the symphysis, ending below in the mental protuberance, the incisive fossa, the mental 

 foramen, and the external oblique line, leading upwards and backwards to become 

 continuous with the front edge of the coronoid process. 



The body of the bone is mainly concerned with the support of the structures in 

 the mouth. 



The Mylo-hyoid forms the muscular floor of the mouth, and thus the mylo-hyoid 

 ridge or internal oblique line can be taken to divide the inner surface of the body of 

 the bone into an upper (or buccal) area and a lower (or cervical) portion. These two 

 ' parts can only come into relation with structures that lie on the corresponding surfaces 

 of the Mylo-hyoid : thus the continuation of the ridge forward would pass below 

 the genial tubercles, because these are for " buccal " structures. 



Owing to the obliquity of its line of origin the mylo-hyoid muscle, passing to the 



