ig 
140 OSTEOLOGY. 
aperture the mental vessels and nerves reach the surface. The upper border 
supports the sixteen teeth of the lower jaw. 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 external oblique ‘line the bone is full and 
rounded, and ends below in the inferior border or base. This slopes outwards at the 
sides, and forwards in front, where it is thick and hollowed out on either side of 
the symphysis to form the digastric fosse (fossze 
digastric), to which the anterior bellies of the 
digastric muscles are attached; narrowing some- 
what behind this, the inferior border again ex- 
pands 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 deep or inner surface - 
of the body is crossed by the internal oblique line 
or mylo- hyoid ridge (linea mylo-hyoidea). This 
slants from above downwards and forwards towards 
aly 
the lower part of the symphysis. It serves for 
the origin of the 
mylo-hyoid mus- 
: 1 13 
cle, and also fur- 
nishes an attach- 
ment to the a 
superior constric- 
torof the pharynx 4 
just behind the 
last molar tooth. 3 
Below the hinder 
part of this ridge 
a ad 9 
the surface is ~ 
hollowed to form ‘ | 
a fossa for the ~ aS ud? ae 
: Fic. 111.—THE INNER SIDE OF THE RIGHT HALF OF THE LOWER JAW. 
lodgment of the ae als i heen 
ee oie wx, 1. Genio-hyoid muscle. . Coronoid process. 5. Angle. 
submaxillar J 2. Mental spines. 9. Sigmoid notch. 16. Fossa for submaxillary 
eland. Above the 3. Genio-hyoglossus 10. External pterygoid gland. 
fore part ot the muscle. muscle. 17. Superior constrictor. 
: e ic 4. Surface in relation to 11. Condyles. 18. Internal oblique line. 
internal oblique the sublingual gland. 12. Inferior dentalforamen. 19. Mylo-hyoid muscle. 
line, the bone is 5, Alveolar border. 13. Mylo-hyoid groove. 20. Digastric muscle. 
smooth and 6. Lingula. 14. Internal pterygoid 21. Digastric fossa. 
7. Temporal muscle. muscle. 
usually convex. 
Here the sublingual gland lies in relation to it. In the angle formed by the 
convergence of the two internal oblique lines, and in correspondence with the back 
of the lower part of the symphysis, there is a raised tubercle surmounted by two 
laterally placed spines, the mental or genial spines (spince mentales). Occasionally 
these are again subdivided into an upper and lower pair, or it may be that the 
lower pair may fuse to form a rough median ridge. To the upper pair of spines 
the genio-hyoglossi muscles are attached, whilst the lower pair serve for the origin 
of the genio- -hy oid muscles. Immediately above the tubercle there is a median 
foramen for the transmission of a nutrient vessel, and close to the alveolar border 
opposite the intervals between the central and lateral incisors, there are two little 
vascular canals. 
The ramus (ramus mandibule) passes upwards from the back part of the bone, 
forming by the junction of its posterior border with the base of the body the angle 
(angulus mandibule), which is usually rounded and more or less everted. The 
outer surface of the ramus affords attachment to the masseter muscle, and when 
