ORGANS OF MASTICATION. 315 



animal this does not appear, the space being occupied by the 

 masseter muscles. 



The lips greatly assist in gathering together the food, and 

 are largely furnished with the nerves of feeling ; they are 

 composed of skin, muscle, and membrane, and possess the 

 powers of motion and sensation in a high degree. 



The mouth is abundantly supplied with a watery fluid 

 called saliva, particularly during mastication, when it is se- 

 creted and poured in in considerable quantities. This fluid 

 is principally secreted by three pairs of glands, the largest 

 of which are the parotid, situated at the root of each ear, 

 and from which two ducts on each side convey the fluid and 

 unite in one previous to entering the mouth. The submaxil- 

 lary glands are situated under the jaws, and their ducts ter- 

 minate in tubular eminences near the fraenum or bridle of the 

 tongue. The other salivary glands are the suhlinguul, situ- 

 ated under the tongue : its ducts terminate rather higher up 

 than those last described. Besides these there are other 

 small glands connected with the cheek and the bottom of 

 the mouth ; and one peculiar to sheep situated behind the 

 lower jaw, and extending towards the eye, and communica- 

 ting with the mouth by means of a duct opening near the last 

 molar tooth. There is thus from these various sources an 

 abundant supply of saliva more copious than most animals 

 possess, and which is rendered necessary by the hard and 

 woody nature of the food consumed in a natural state. And 

 it has been found that a large supply passes into the stomach 

 independent of mastication, and is there required for softening 

 and macerating the dry food ; for, when deprived of this sup- 

 ply by an experiment, it has been found that the contents of 

 the paunch remained dry. 



The mouth is principally filled with the tongue, which is 

 muscular in its structure and very flexible, being, indeed, a 

 principal agent in mastication and swallowing. It is larger 

 at the upper part than towards its tip, and is confined poste- 

 riorly to the muscles between the branches of the lower jaw, 

 by a sort of fleshy bridle, and above to a singularly shaped 

 bone called the os hyoides. It possesses both the power of 

 feeling and tasting, and for this purpose is well supplied with 

 two descriptions of nerves, and is covered by both cutis and 

 cuticle. 



There is a marked distinction in the back part of the 

 mouth between the horse and the sheep and other rumina- 



