210 BONES OF THE FACE. 



nal surface is an oblique ridge running backwards and 

 upwards to the root of the coronoid process, to which is 

 attached the depressor-anguli oris and platzsma in front, 

 and the masseter muscle behind. 



On the internal surface is also an oblique ridge, called 

 the mylo-hyoid ridge, which gives attachment to the mylo- 

 hyoid muscle in front, and the superior constrictor of the 

 pharynx and intermaxillary ligament behind. Beneath 

 this ridge is a groove for the mylo-hyoid nerve, and below 

 this an oblong depression for the sub-maxillary gland. 

 The lower border of the jaw, called the base, is thick and 

 rounded. The upper border is the alveolar arch, having 

 its alveolar processes and cavities corresponding to the va- 

 riety of teeth they receive. The alveolar cavity of the mid- 

 dle incisor has its antero-posterior diameter the broadest, 

 and the septum between it and its fellow thicker than that 

 separating it from the lateral. The alveolus of the lateral 

 incisor has its opening wider in front than behind, and is 

 described as being indented on its outer side. Its anterior 

 wall is a little convex, the posterior concave, and its late- 

 ral septa thicker behind than in front. 



The alveolus of the canine is found to be larger than that of 

 either the incisors or bicuspids. Its form is conical, with the 

 sides compressed and presenting, laterally, a depression cor- 

 responding to the root of the tooth. Its anterior wall is said 

 to be more prominent and thinner than any other in the 

 dental arch, and looks backwards and downwards, while 

 the posterior is directly vertical. The axis of the canine 

 is forwards and upwards, and the opening of its alveolus 

 is said to be twice the breadth in front that it is behind. 

 Its form is oval. 



The alveolus of the first bicuspid has its form conical, its 

 sides compressed, its outer surface flat, and its inner rather 

 concave. It is smaller than the canine, has its opening oval, 

 with edges in front and behind seen to be a little indented. 

 Its antero-posterior diameter looks outwards and forwards, 

 its vertical obliquely inwards. 



The alveolus of the second bicuspidh&s its vertical axis look- 



