. Animal physiology. Physiology, Comparative; Physiology, Comparative. 154 MOTIONS OF JAW. INSALIVATION. and is hence called the temporal muscle. It covers at its origin a large surface of bone; but its fibres approach one another as they descend, and pass under a bony arch (which may be felt between the cheek and the ear), to attach themselves to a pro- , 7y, ^ cess or projection of the lower jaw (a, Fig. 104), about an inch in front of the joint. As the distance from the fulcrum, of the point at which the power is applied, is thus much less than that of the front of the jaw, where chiefly th
. Animal physiology. Physiology, Comparative; Physiology, Comparative. 154 MOTIONS OF JAW. INSALIVATION. and is hence called the temporal muscle. It covers at its origin a large surface of bone; but its fibres approach one another as they descend, and pass under a bony arch (which may be felt between the cheek and the ear), to attach themselves to a pro- , 7y, ^ cess or projection of the lower jaw (a, Fig. 104), about an inch in front of the joint. As the distance from the fulcrum, of the point at which the power is applied, is thus much less than that of the front of the jaw, where chiefly the re- sistance is encountered, the power of the muscle is applied at a me- chanical disadvantage; and, to. overcome a given resistance, the Fig. 104. muscle must itself be several times more powerful. Thus the tiger and lion, which can lift and carry away the bodies of animals weighing several hundred pounds, must possess temporal muscles that shall contract with a force of two thousand, or even more (Mechanical Philosophy, §. 292). Insalivation. 190. The act of mastication is connected with another; which is also of great importance in preparing for the subsequent process of digestion. This is the blending of the saliva with the food, during its reduction between the teeth,—an act which is termed insalivation. The saliva is separated from the blood, by glands which are situated in the neighbourhood of the mouth; of these there are three pair in man, two beneath the tongue (Fig. 105), and one in the cheek, each pouring in its secretion by a separate canal. The salivary fluid is principally composed of water, in which a small quantity of animal matter and some saline substances (chiefly common salt) are dissolved ; the whole amount of these, however, is not more than 1 part in 100. The secretion of saliva is not constantly going on; but the fluid is formed as it is The stimulus by which the gland is set. Please note that these images are extracted from scanned page i
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