CHAP, in.] SKELETON OE THE HEAD AND TRUNK. 77 



with the palatine plates of the maxillae and palatines. Its posterior 

 margin is free, and forms the liinder end of the lower part of the 

 internasal septum. 



^ 37. The skeleton of the lower jaw, or iMaxdible, consists of 

 two bones, which meet together in front at an acute angle. Each 

 bone, i.e., each half of the mandible, consists of two parts — its hinder, 

 vertically expanded portion, being called the asccndi)u/ ramus {ar), 

 while the rest is named the horizontal ramus (hr). The horizontal 

 ramus is almost of the same depth throughout, and slightly curved — 

 its upper margin being concave, and its lower margin convex. The 

 latter is smooth and rounded, but the upper edge is festooned by 

 unequal cavities, forming sockets for the lower teeth. The place of 

 junction of the two horizontal rami is called the symphysis (sy), and 

 presents a very rough surface. The horizontal ramus begins to 

 expand into the ascendmg ramus immediately behind the last tooth, 

 and becomes a triangular plate of bone, concave externally, and 

 with three prominences, separated by two concavities, on its hinder 

 margin. 



The highest of these prominences (which is also the highest part 

 of the mandible) is called the coronoid process, and is a vertical plate 

 of bone (e). The second prominence (separated from the preceding 

 by a considerable interval) is the condyle of the mandible, and is a 

 transversely- extended convex articular surface (y), destined to fit 

 into the glenoid fossa of the temporal bone. The piece of bone 

 which immediately supports the condyle is termed the neck. The 

 third and lowest prominence (separated from the condyle but by a 

 narrow interval) is termed the angle {an), and is a small, vertically- 

 extended process, on a line with the inferior margin of the horizontal 

 ramus. 



The coronoid process rises even a little more above the condyle 

 than does the latter above the angle, and has inserted into it the 

 temporal muscle. 



The deep fossa outside the ascending ramus (Fig. 46, ar), the 

 ridge beneath it and the angle, have inserted into them a muscle, 

 called the masseter. The symphysis is convex and very obHque, 

 being inclined strongly backwards as well as downwards. 



The outer surface of the horizontal ramus is convex, its inner 

 surface is flattened. On the inner side of the ascending ramus, 

 below the level of the condyle, is a considerable foramen, called the 

 inferior dental (14). This leads into the " dental canal," do's^Ti which 

 the dental nerves and vessels pass. 



At the more anterior part of the outer side of the horizontal ramus 

 are a pair of small foramina (Fig. 46, i^), called the mental foramina. 

 They transmit branches of the inferior dental nerve and artery. 



Behind the symphysis, towards its lower end, is a small depression 

 serving for the insertion of the digastric muscle. 



§ 38. The HTOiD apparatus is a complex structure, consisting of 

 two long jointed bony bars {t-- to cli), "the anterior cor)iua," and 

 two short unjointed bony bars {th), " the jjosterior cornua " — both an 



