. Animal physiology. Physiology, Comparative; Physiology, Comparative. MUSCLES OP THE FACE. 459 continually reminded of the loss of mechanical power which results from this, by our inability to exercise the same force with our front teeth, that we can employ with the back. Thus, when we wish to crack a nut, or to crush any hard substance between the teeth, we almost instinctively carry it to the back of the jaws, so as to be nearer the joint, and thus to receive more of the power of the muscle. 624. The general arrangement of the chief muscles of the face is seen in Fig, 212. The largest is th
. Animal physiology. Physiology, Comparative; Physiology, Comparative. MUSCLES OP THE FACE. 459 continually reminded of the loss of mechanical power which results from this, by our inability to exercise the same force with our front teeth, that we can employ with the back. Thus, when we wish to crack a nut, or to crush any hard substance between the teeth, we almost instinctively carry it to the back of the jaws, so as to be nearer the joint, and thus to receive more of the power of the muscle. 624. The general arrangement of the chief muscles of the face is seen in Fig, 212. The largest is the * temporal muscle, t, the fibres of which arise from an extensive surface of the parietal and temporal bones, and then converge or ap- proach each other, passing under the bony arch or zygoma, z (which is partly formed by a process from the temporal bone, and partly by the malar or cheek bone), to be attached to the coronoid process of the lower jaw. This muscle is of ex- traordinary power in those beasts of prey, which lift and drag heavy carcases in their jaws ; and in those which (like the Hyasna) obtain their support by crushing the bones which others have left. It is assisted by the masseter muscle, m, which passes from the zygomatic arch and cheek-bone, to the angle of the lower jaw ; and also by other muscles. Besides these, the figure shows the ring-like muscle or sphincter, o, which sur- rounds the opening of the eye, and serves by its contraction to close the lids ; and also the similar muscle, 5,6, which surrounds the mouth, and draws together the lips. The antagonists to these are several small muscles, which form the fleshy part of the face, and produce the various changes by which its expression is given. These muscles are more numerous in Man and the Monkey tribe than in any other animals. 6*25. Besides the 22 bones of which the skull is properly composed, we may reckon as belonging to it the four small bones which form part of the apparatus of hearing (§. 516
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