. Human physiology : designed for colleges and the higher classes in schools, and for general reading. for example, in the limbs, as to give them both free-dom of motion and beauty of form. The muscles that movethe fingers help to make up the full part of the arm, whiletheir slender tendons occupy but little space as they play overthe bones of the wrist. If there were no tendons, and themuscles were extended to the parts which they move, the handwould be a large cumbrous mass, instead of the light and agilething that it is now. For the muscles would of necessity becontinued of their full size,
. Human physiology : designed for colleges and the higher classes in schools, and for general reading. for example, in the limbs, as to give them both free-dom of motion and beauty of form. The muscles that movethe fingers help to make up the full part of the arm, whiletheir slender tendons occupy but little space as they play overthe bones of the wrist. If there were no tendons, and themuscles were extended to the parts which they move, the handwould be a large cumbrous mass, instead of the light and agilething that it is now. For the muscles would of necessity becontinued of their full size, and, therefore, the bones would ofcourse be very large in order to afford an attachment to themuscles. 296. In the action of the muscles upon the bones, we havo 17* 198 HUMAN PHYSIOLOGY. The three kinds of lever exemplified in the action of muscles. examples of the three kinds of levers treated of in natural phi-losophy. Some of these I will now notice. The first kind oflever has the fulcrum between the weight and the power, asrepresented in Fig. 107. F is the fulcrum, W the weight, and FIG. FIRST KIND OF LEVER. P the power. You have examples of this lever in the commonpump handle, the beam of a pair of scales, the crowbar, ascommonly used, scissors, &c. You have an example of this formof lever in the human body, in the action of the muscles inmoving the head back and forth on the top of the spinalcolumn. In this case, when the head is moved forward, thetop of the spine is the fulcrum, the weight to be moved is theback of the head, and the power is the contraction of the musclesthat bow the head forward. When the head is bent backward,the power is the contraction of the muscles behind, and theweight is the front part of the head. The muscles that movethe head backward are stronger than those that move it for-ward. It is necessary that it should be so, for there is more ofthe head in front of the point of support or fulcrum than thereis behind it. Hence, when sleep relaxe
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