THE ORGANS OF DIGESTION. 377 



and bladder arc, perhaps, not .properly organs of digestion, as 

 their action is rather upon the blood than on those fluids 

 formed of the food taken by the animal. But it is convenient 

 to describe them under this head. For the same reason I shall 

 describe the peritoneum, or investing membrane of the bowels, 

 in this chapter. 



The llj)s are two in number, the upper and lower. They 

 are composed of masses of elastic cellular tissue, small mus- 

 cles, and glands. They are partly covered by skin, and on 

 their inside starts the mucous membrane which lines the in- 

 side of the entire alimentary canal. The lips of the horse 

 serve to grasp the food and bring it within the mouth. 



The teeth have been described in another part of this work. 

 I shall only consider them here as concerned in preparing the 

 food for the system. The front teeth are for cutting the food, 

 and the back teeth for grinding it. 



The tongue is a large, muscular organ situated in the lower 

 part of the cavity of the mouth. It is attached by its roots to 

 the hyoid bone, or bone of the tongue, and along the under 

 side of its body to the lower jaws. Its forward part is free. 

 It is the organ of taste, and its use is to move food about in 

 the mouth during the process of chewing, and to carry the 

 parts which are sufficiently masticated back into the pharynx 

 to be swallowed. It is not the only organ having nerves of 

 taste. The palate, pharynx, and, probably, the gullet, have 

 some nerves of taste. 



The salivarij glands are six in number, three on each side of 

 the mouth. They are named the sublingual, the submaxillary, 

 and the parotid glands. 



The sublingual glands are situated under and one at each 

 side of the tongue. They are the smallest of the salivary 

 glands. Each gland has little ducts, or tubes, leading from it, 

 and opening into the cavity of the mouth. The ducts of the 

 sublingual glands open under the fore-part of the tongue. 



The submaxillary glands, one on the inside of the turn of each 



