320 PHILOSOPHY OF ZOOLOGY. 
the food which it contains more immediately m contact 
with the mouth. Tubes are used for this purpose among 
the mollusca, and circular moveable cilize m 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 frout, 
with sharp edges, are given to many quadrupeds for the 
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 kmd 
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 jomt 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 
