MAXILLA INFERIOR. 97 



denominated the base, is round and firm, except at the angles, 

 where it is thin. 



The angle is formed at the posterior extremity of the base : 

 in children it is obtuse ; but in adults whose teeth are perfect, 

 it is nearly rectangular. The masseter muscle is inserted into 

 the lower jaw, at the angle ; and there are several inequalities 

 on the surface made by this muscle. 



Fig. 22.* The anterior or coronoid 



process, is rather higher than 

 the posterior, and forms an 

 obtuse point : into this process 

 the temporal muscle is inserted. 

 The anterior edge of the coro- 

 noid process is sharp, and con- 

 tinued into the rid^e above 



O 



mentioned ; from this edge the 

 buccinator muscle arises. As 

 the alveoli are on the inside of 

 this edge and ridge, the jaw is very thick at this place. There 

 is a semicircular or sigmoid notch between this coronoid process 

 and the posterior or condyloid ; and here the bone is very thin. 



The condyles are oblong, and are placed obliquely ; so that 

 their longest axes, if extended until they intersect each other, 

 would form an angle of more than one hundred and forty 

 degrees. The neck of the process, or the part immediately 

 below the condyle, is concave on the anterior, arid convex on 

 the posterior surface. 



On the inside of the jaw, in the middle of the chin, is a small 

 protuberance, sometimes divided by a vertical fissure ; to this 

 are attached the fraenum lingua, and some muscles of the 

 tongue and os hyoides. Farther back is a ridge called the 

 mylo-hyoid, which extends backwards and upwards, until it 



* The lower jaw. 1. The body. 2. The ramus. 3. Thesymphysis. 4. The 

 fossa for the depressor labii inferioris muscle. 5. The mental foramen. 6. The 

 external oblique ridge. 7. The groove for the facial artery. 8. The angle. 9. 

 The extremity of the mylo-hyoidean ridge. 10. The coronoid process. 11. The 

 condyle. 12. The sigmoid notch. 13. The inferior dental foramen. 14. The 

 mylo-hyoidean groove. 15. The alveolar process. . The middle and lateral 

 incisor tooth of one side. c. The canine tooth, b. The two bicuspides. m. The 

 three molares. 



9 



