320 PHILOSOPHY OF ZOOLOGY. 



the food which it contains more immediately in contact 

 with the mouth. Tubes are used for this purpose among 

 the mollusca, and circular moveable cilia3 in some of the in- 

 fusory animalcula. 



Where the food is soft, and easily broken or torn, and 

 where the lips have sufficient strength, the mouth is easily 

 filled with food. But where the animals are weak, or the 

 portion of the food for mastication difficult to be separated,, 

 other means are provided than those to which we have al- 

 ready referred. The lips, as in the case of the mandibles 

 of birds, are covered with a horny shell, 'admirably adapt- 

 ed for cutting off portions of food. Teeth placed in front, 

 with sharp edges,- are given to many quadrupeds for tlie 

 same end ; and are termed., from their use, cutting teeth. ' 

 By these various contrivances, the food is brought in 

 contact with the mouth ; and the requisite quantity separa- 

 ted from the mass. The cavity of the mouth, in the most 

 perfect animals, is formed by the lips in front, the hard 

 palate above, the soft palate behind, the tongue below, and 

 the cheeks on each side. All these parts contribute to mo- 

 dify the motions of the food, while retained in the cavity. 

 In some cases, the food, upon entering the mouth, is con- 

 veyed immediately into the gullet; while in many animals 

 it is subjected to the process of mastication or chewing. 

 For this purpose, the under jaw is indispensably necessary ; 

 and the motions of which it is susceptible indicate the kind 

 of action which is performed. When the jaw is articulat- 

 ed in such a manner, that a vertical motion only is permit- 

 ted, we may infer, that the food consists chiefly, if not ex- 

 clusively, of flesh. If, on the other hand, the joint admits 

 both of a vertical and horizontal motion, the food consists 

 chiefly of vegetables. Between these two extremes there 

 are many intermediate modifications, enabling certain ani- 

 mals to, feed on both kinds of food. With each condition of 



