THE MAXILLARY BONES. 35 



In ordinary mastication the various movements are com- 

 bined in every possible manner. 



When the mouth is widely open the condyles play upon 

 the articular eminence in front of the glenoid cavity, and 

 the external pterygoid, which assists in widely opening the 

 mouth, draws not only the condyle, but also the inter- 

 articular nbro-cartilage forwards, so that the latter still 

 intervenes between the condyle and the articular eminence. 

 The interarticular cartilages do not, however, accompany 

 the jaw in its extreme movement, but are believed only 

 to pass forwards as far as that part of the eminence which 

 is slightly hollowed out. As, however, in dislocation the} 7 

 accompany the condyles, this supposition may be incorrect. 



The position of repose is neither complete closure nor 

 opening of the jaws : in persons with enlarged tonsils the 

 habitual position is one with the mouth somewhat more 

 widely open, owing to the difficulty of breathing through the 

 nose ; a fact which often causes an irregularity in the 

 disposition of the teeth. 



The axis on which the jaw moves is, owing to the bend 

 of the ramus, far behind the glenoid cavity; it lies very 

 nearly in a plane formed by prolonging the plane of the 

 masticating surface of the teeth. 



The .motions executed in mastication differ much according 

 to the nature of the food ; hence it happens that in different 

 animals the muscles of mastication are very variously 

 developed. 



Thus, in the Herbivora, which move their jaws greatly 

 from side to side, as any one may observe for himself, the 

 pterygoids, and especially the external pterygoid, attain to 

 a very large relative size. 



On the other hand, in the Rodents, which move their 

 jaws backward and forwards in gnawing, the masse ter is 

 enormously developed, and has a very marked general 

 backward direction. 



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