ii8 A MANUAL OF ANATOMY 



The ramus rises, at either side, from the extremity of the body. 

 It is compressed from without inwards and presents two surfaces 

 and four borders. The external surface gives insertion to the 

 masseter, and, in the vicinity of the angle, it presents a few oblique 

 ridges for the tendinous bands of that muscle. The internal 

 surface presents, a little below its centre, the inferior dental foramen, 

 which is on a level with the summit of the crown of the third molar 

 tooth. This foramen leads to the dental canal, which traverses 

 the bone to near the symphysis, and from which, near its anterior 

 part, the mental foramen opens on the external surface. This 

 canal lodges the inferior dental nerve and vessels, and communicates 

 with the foramina which open on the extremities of the fangs of 

 the teeth. The inferior dental foramen presents anteriorly and 

 internally a thin, sharp plate of bone, called the lingula. Behind 

 the lower end of the latter is a short crescentic margin on the inner 

 aspect of the foramen, and proceeding downwards and forwards 

 from this is the mylo-hyoid groove, which terminates a little below 

 the posterior extremity of the mylo-hyoid ridge, and transmits 

 the mylo-hyoid nerve and artery. The spheno -mandibular liga- 

 ment is attached to the lingula and to the crescentic margin behind 

 it. Between the inferior dental foramen and the angle there is a 

 rough impression, often strongly ridged, which gives insertion to 

 the internal pterygoid. 



The anterior border is continuous with the external oblique line 

 opposite the third molar alveolus, and is shorter than the posterior. 

 The posterior border meets the inferior border, thus forming the 

 angle, which, in muscular subjects, is strongly marked and slightly 

 everted. Externally and internally it presents rough impressions 

 for portions of the masseter and internal pterygoid respectively, 

 and between these muscles it gives attachment to the stylo-man- 

 dibular ligament. The angle is obtuse, and in the adult amounts on 

 an average to 120 degrees. In early infancy it is as much as 150 

 degrees, and in old age it amounts to about 140 degrees. The 

 inferior border is continuous with the inferior border or base of 

 the body. The superior border presents the sigmoid notch, the 

 coronoid process, and the condyle. 



The sigmoid notch communicates with the zygomatic fossa, and 

 transmits the masseteric nerve and artery to the deep surface of 

 the masseter. 



The coronoid process surmounts the anterior border of the ramus, 

 and is triangular and compressed from without inwards. Its 

 external surface gives insertion to fibres of the masseter, and its 

 internal surface, as well as the superior and anterior borders, to 

 part of the temporal muscle. The internal surface is marked by 

 a ridge which extends downwards on the internal surface of the 

 ramus, not far from the anterior border, to a point on the inner side 

 of the last molar alveolus, where it becomes continuous with the 

 mylo-hyoid ridge. The temporal muscle continues to take inser- 

 tion into this ridge, as well as into the elongated triangular depres- 

 sion between it and the anterior border of the ramus. 



