Human physiology : designed for colleges and the higher classes in schools and for general reading . es drawing down the jaw. If while the jawbe held fast by muscles which draw it upward, the digastriccontracts, it will draw up, as you can readily see by the Figure,the hyoid bone, c, and with it, of course, the larynx which is at- 208 HUMAN PHYSIOLOGY. Straight and oblique muscles of the eye. tached to it. Now precisely this set of motions occurs when weswallow. The mouth is shut by the drawing up of the jaw,and then the contraction of the digastric muscle draws up thelarynx, as you can percei
Human physiology : designed for colleges and the higher classes in schools and for general reading . es drawing down the jaw. If while the jawbe held fast by muscles which draw it upward, the digastriccontracts, it will draw up, as you can readily see by the Figure,the hyoid bone, c, and with it, of course, the larynx which is at- 208 HUMAN PHYSIOLOGY. Straight and oblique muscles of the eye. tached to it. Now precisely this set of motions occurs when weswallow. The mouth is shut by the drawing up of the jaw,and then the contraction of the digastric muscle draws up thelarynx, as you can perceive if you place your fingers on thelarynx, or Adams apple, as it is called, when you perform theact of swallowing. The little muscle in which the loop is,renders some assistance to the digastric in thus drawing up thehyoid bone and the larynx, as you can see by the Figure. 307. I will notice one more example of the pulley-ar-rangement. It is in the eye. There are six muscles thatmove the eye-ball. Five of them are represented in Fig. are four straight muscles, three of which are marked. a, 6, c; the fourth is behind 6, the upper edge of it onlybeing seen in the Figure. These muscles are at their origin inthe back part of the socket of the eye arranged round the opticnerve, and passing forward are attached to the sclerotic coat,the firm white coat of the eye. The two lateral muscles, b, andits opposite, move the eye to the one side and the other, andthe two muscles, a and c, perform the up and down there are certain oblique rolling motions of the eyeballwhich can not be executed by these straight muscles. For thesemotions two muscles are provided, one of which has a pulley-arrangement, as represented in the Figure. This muscle, s, hasa long tendon which passes through a ring in cartilage in theroof of the socket, and then turning back is fastened as you seeto the upper part of the eyeball. This muscle, as stated in thechapter on the Nervous System, is under
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