132 ANIMAL DENTISTRY. 



and drawn to either side at will. In ruminants the lateral 

 motion is pronounced while in the carnivora it is prevented 

 by the interlocking of the canine teeth, the beveled molars 

 and the ginglymoid character of the articulation. In soli- 

 peds the lateral motion is nominal. The antero-posterior 

 motion is prominent in rodents and is possible to a normal 

 degree in herbivora. The upward movement, which is the 

 most forcible, is of course a prominent movement in all 

 animals, but is an exceptionally powerful one in the solipeds 

 and ruminants. 



Mastication is efifected in about the following manner. 

 The mouth is opened by gravity, aided by the stylo-maxil- 

 laris and digastricus muscles; it is then swung to the side 

 and slightly forward by the pterygoids, temporalis and mas- 

 seter, and then diagonally upward by the combined effort of 

 the masseter, internal pterygoid and temporalis. During 

 these movements the tongue and buccinator are engaged in 

 keeping the bolus in position to be caught between the teeth 

 as they come together. 



Mastication is unilateral, only one side of the mouth is 

 used at a time. Herbivora will chew on one side for a few 

 minutes and then shift the next bolus to the other, at their 

 will. 



