MASTICATION AND DEGLUTITION. 



69 



fering conspicuously from those of other mammalia, by possessing 

 gibbous apices excessively obtuse. 



The four central teeth in both jaws are 

 the incisores : the outer one on each side 

 in both is the canine : the five outermost 

 on each side in both are the molares. 



a, belly of the digastric arising at the 

 root of the mastoid process of the tempo- 

 ral bone : b, belly arising below the sym- 

 physis of the lower jaw: c, tendon in 

 which each ends : d, os hyoides, into 

 which the tendon is inserted. If the os 

 hyoides is fixed, the inner belly can lower 

 the jaw : if the jaw is fixed, the os hy- 

 oides can be raised, e, genio-hyoideus : 

 f, mylo-hyoideus. 



" The lower jaw is connected with the skull by a remarkable 

 articulation, which holds a middle rank between arthrodia and 

 ginglymus; and, being supplied with two cartilaginous menisci 

 of considerable strength, has easy motion in every direction." In 

 other words, the condyles of the lower jaw are prevented from 

 descending very deeply into the glenoid cavity ; and are con- 

 fined to vertical movements, by a cartilage which is hollow on 

 each surface, and moveable, and permits the condyle to move 

 from the glenoid cavity to a tubercle which stands before this, 

 and thus to acquire still greater mobility. 



a, outer part of the lower 

 jaw : by its condyle, pulled 

 down from the glenoid cavity 

 to show the joints : c, inter- 

 articular fibro-cartilage form- 

 ing two menisci : rf, upper 

 synovial membrane : e, lower 

 synovial membrane : f, zygo- 

 ma, : g, mastoid process : k, sty- 

 loid process. The three other 

 figures are a superior, an in- 

 ferior, and a lateral, view of the 

 interarticular cartilage. , 



The digaster, assisted somewhat by the genio-hyoidei and 



