62 THE HORSE IN HEALTH AND DISEASE 



The mouth is a cylindric cavity situated between the two 

 jaws, elongated in the direction of the long axis of the head. It 

 has an anterior opening for the introduction of food, and a posterior 

 one to communicate with the pharynx. When closed, the mouth 

 is nearly filled up by the teeth and tongue. 



The lips are designated superior and inferior from their posi- 

 tions. On the outer surface of the Ups are found many fine, short 

 hairs; also a number of long bristle-like hairs of a tactile nature. 

 The inner surface is lined with mucous membrane, which is smooth 

 and usually of a pink color. The function of the hps is the pre- 

 hension of foods. They also assist in keeping the food in the 

 mouth during mastication. If the nerves supplying the Ups are 

 cut or severely injured, paralysis results and the horse cannot 

 graze. 



The cheeks are two smooth membranous walls which form 

 the sides of the mouth. They are continuous in front with the 

 lips; above and below, with the gums. They are very active 

 agents in the mastication of food, and constantly push the food 

 between the teeth. Numerous secreting glands are found in the 

 cheeks. 



The tongue extends from the back part of the mouth to the 

 incisor teeth. It is a freely movable muscular organ. Some of 

 its muscles are directed longitudinally, others vertically, and still 

 others transversely. This arrangement affords the organ extensive 

 movement in all directions. For description, it may be divided into 

 tip, body, and root. The tip is free and can be extruded from the 

 mouth. The body is the main part, and is covered superiorly with 

 fine, file-like elevations, termed "papillae." Near the back part 

 of the tongue there are two large circumvallate papillae in which 

 the taste-buds are found. The root is inserted into the lingual 

 process of the hyoid bone. The function of the tongue is the 

 prehension of liquids. It also assists in mastication by keeping 

 the food between the teeth. During the act of swallowing it 

 performs the important duty of a piston, and moves back and forth 

 with each swallow of fluid. 



The teeth are classified according to form and position into: 

 Incisors, situated in front, implanted in the premaxillse and the 

 body of the mandible; canines, situated a little further back, nearer 

 the incisors in the lower jaw than in the upper; moZars, which occupy 

 the side of the dental arch and are often termed "the grinders" (Fig. 



