. Human physiology : designed for colleges and the higher classes in schools, and for general reading. f 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 st
. Human physiology : designed for colleges and the higher classes in schools, and for general reading. f 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 relaxes the muscles, if we aresitting up the head falls forward. 297. In the second kind of lever the weight is between thefulcrum and the power, as represented in Fig. 108. The com-mon wheelbarrow is an example of this form of lever. Youhave an example of it in the body in the raising of the heel FIG. SECOND KIND OF LEVER. THE MUSCLES. iy» Motion of the foot in walking. from the ground in walking. In doing this the to beraised is the whole body, the foot being the lever, and theforward part of the foot being the fulcrum. This will be madetlear by Fig. 109. W is the large bone of the leg sustaining FIG. 109.
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