26 PHYSIOLOGY OP FARM ANIMALS [CH. 



for collecting the food, and for this purpose they are strong and 

 thick and are richly supplied with end organs or organs of touch. 

 The lips are not used by a horse when grazing, but are drawn 

 back so as to allow the incisor teeth to bite off the grass. In 

 the ox the lips play a small part, but the tongue is used freely, 

 being first protruded and curled round the grass, and then with- 

 drawn into the mouth, whUe the grass is cut off between the 

 incisor teeth of the lower jaw, and the dental pad which takes 

 the place of the teeth m the upper jaw. In the sheep and goat 

 the upper lip is divided mto two parts each of which is possessed 

 of independent movement. As m the ox the lower incisors bite 

 against a pad in the upper jaw, there being no upper incisors. 

 By reason of the cleft upper lip the sheep and the goat can bite 

 more closely to the ground, and thus they can get a living where 

 a horse or an ox could not do so. In all these animals the tongue 

 is employed in pressing back the food to the hinder part of the 

 mouth where it is brought under the action of the molar teeth. 

 The tongue is assisted in most animals by grooves in the palate. 

 In the ox there are papillae covering the inside of the mouth and 

 inclining backwards. The object of these is believed to be to 

 assist in preventing the food from falling out of the mouth. 



The tongue differs considerably in the horse and the ox; in 

 the former animal it is relatively smooth and swells out at the 

 apex, in the latter it narrows from the base to the apex, being 

 pointed ; moreover it is very rough and well able to resist injury 

 from coarse grasses. The movements of the tongue may be very 

 extensive in the ox and the dog, but horses seldom protrude 

 their tongues. 



The process of mastication is very effectively carried out in 

 all herbivorous animals, for the molar teeth, by reason of the 

 hard enamel ridges separated by the softer cement substance, 

 wear with a rough surface, and are admirably adapted for grind- 

 ing and crushing the food 



The lower incisor teeth in those animals in which there is a 

 dental pad are placed obliquely in the jaw so that the pad is not 

 injured when the mouth closes. For the same reason they are 

 capable of free movements in their sockets. In the horse the 

 incisors in both jaws are at first vertical, but become oblique 

 with advancing age. All the teeth are gradually pushed out 

 from their sockets, the fangs becoming reduced in length; at 



