DISEASES OF THE JAWS. 67 



or if the teeth are incapacitated from any circumstance, so 

 that hay or any other food escapes grinding, the animal falls 

 off in condition. 



In ruminating animals the act of chewing is very rapid 

 and incomplete whilst the collection of food is going on, but 

 there is a very slow and perfect mastication when the 

 aliment is returned to the mouth during rumination. 



Carnivorous animals do not enjoy this lateral movement, 

 from the fixed nature of the joint between the jaws, as well 

 as the manner in which the teeth fix into each other, and do 

 not present a surface for free lateral friction. 



The teeth are therefore adapted for the perforation of flesh 

 by a simple closure of the jaws in all carnivora*, whereas they 

 are truly grinders in the herbivora. The tongue, in connec- 

 tion with mastication, rolls the food from side to side, and 

 from before back, whereas the cheeks, also endowed with 

 muscular power, press the food between the molars. 



DISEASES OF, AND INJURIES TO, THE ORGANS OF 

 MASTICAHON. 



INJURIES INFLICTED ON THE JOINT BETWEEN THE TEMPORAL 

 BONE AND LOWER JAW. This joint is broad, well protected, 

 and so formed as to render it not very liable to injury or 

 disease, which, whenever present, is attended with much 

 danger. In man, and some of the lower animals, dislocation 

 backwards is possible. This is an accident unknown in the 

 horse and large herbivorous quadrupeds. It is of extreme 

 rarity even in the dog and cat, and occurs from the lower 

 jaw being accidentally opened wider than is normally ad- 

 mitted by the joint The mouth being forced open in the 

 cruel manner we have seen adopted in giving some animals 

 medicine, is apt to injure the joint. The displacement is 



