

THE MANDIBLE. 



155 



temporal bones. The anterior or horizontal part, which contains the teeth, is 

 called the corpus mandibulae, (body) ; the posterior or vertical portions constitute the 

 rami mandibulse. 



The body displays in the median plane, in front, a faint vertical ridge, the 

 symphysis, which indicates the line of fusion of the two symmetrical halves from 

 which the bone is primarily developed. In- 

 feriorly this ridge divides so as to enclose, in 

 well-marked specimens, a triangular area the 

 protuberantia mentalis (mental protuberance), 

 the centre of which is somewhat depressed, thus 

 emphasising the inferior angles, which are 

 known as the tubera mentalia (mental tubercles). 

 The lateral surface is crossed by a faint, elevated 

 ridge, the linea obliqua (oblique line), which 

 runs upwards and backwards from the mental 

 tubercle to the lower part of the anterior 

 border of the ramus, with which it is conflu- 

 ent. From this 

 ridge arise the m. 

 quadratuslabiiin- 

 ferioris and the tri- 

 angular muscle. 

 A little above this, 

 midway between 3 _ 

 the upper and / 

 lower borders of ^ 

 the mandible, and 

 in line with the 

 root of the second 

 premolar tooth, 

 the bone is pierced 

 by the mental fora- 

 men; this is .the 

 anterior opening 

 of the inferior 



alveolar canal, which traverses the body of the bone. Through this aperture 

 the mental vessels and nerves reach the surface. The upper border supports 

 the sixteen teeth of the mandible. It is thick behind and thinner in front, in 

 correspondence with the size of the roots of the teeth. Anteriorly the sockets 

 of the incisor and canine teeth produce a series of vertical elevations (juga 

 alveolaria), of which that corresponding to the canine tooth is the most prominent. 

 When this is outstanding it gives rise to a hollowing of the surface between 

 it and the symphysis, often referred to as the incisor fossa ; frequently, however, 

 this is only faintly marked. Below the oblique line the bone is full and rounded, 

 and ends below in the basis mandibulsB (inferior border). This slopes laterally 

 at the sides, and forwards in front, where it is thick and hollowed out on either 

 side of the symphysis to form the digastric fossae, to which the anterior 

 bellies of the digastric muscles are attached; narrowing somewhat behind 

 this, the base again expands opposite the molar teeth, and finally becoming 

 reduced in width, terminates posteriorly at the angle formed between it and 

 the posterior border of the ramus. The medial surface of the body is crossed 

 by the mylo-hyoid line. This slants from above downwards and forwards 

 towards the lower part of the symphysis. It serves for the origin of the 

 mylo-hyoid muscle, and also, just behind the last molar tooth, furnishes an 

 attachment to the superior constrictor of the pharynx. Below the posterior part 

 of this ridge the surface is hollowed to form a fossa for the lodgment of the 

 submaxillary gland. Above the anterior part of the mylo-hyoid line the bone is 

 smooth and usually convex. Here the sublingual gland lies in relation to it. 

 In the angle formed by the convergence of the, two mylo-hyoid lines,, and in 



Fia. 164. THE MANDIBLE AS SEEN FROM THE LEFT SIDE. 



1. Mental tubercle. 



2. Mental protuberance. 



3. Symphysis. 



4. Coronoid processes. 



5. Condyloid processes. 



6. Neck. 



7. Angle. 



8. Oblique line. 



9. Mental foramen. 



