478 MUSCLE-NERVE PHYSIOLOGY 



prostrate. As at first, while the calf muscles of one leg and foot are preparing, 

 so to speak, to push the body forward and upward from behind by raising the 

 heel, the muscles on the front of the trunk and the same leg (and of the other leg, 

 except when it is swinging forward (are helping the act by pulling the legs and 

 trunk, so as to made them incline forward, the rotation in the inclining occur- 

 ring mainly at the ankle joint. Two main kinds of leverage, are, therefore, 

 employed in the act of walking, and if this idea be firmly grasped, the details 

 will be understood with comparative ease. One kind of leverage employed 

 in walking is essentially the same with that employed in pulling forward the 

 pole, as in figure 339. And the other, less exactly, is that employed in raising 

 the handles of a wheelbarrow. Now, supposing the lower end of the pole to be 



FIG. 341. 



placed in the barrow, we should have a very rough and inelegant, but not 

 altogether bad representation of the two main levers employed in the act of 

 walking. The body is pulled forward by the muscles in front, much in the 

 same way that the pole might be by the force applied at p, while the raising 

 of the heel and pushing forward of the trunk by the calf muscles are roughly 

 represented on raising the handles of the barrow. The manner in which these 

 actions are performed alternately by each leg, so that one after the other is 

 swung forward to support the trunk, which is at the same time pushed and 

 pulled forward by the muscles of the other, may be gathered from the previous 

 description. 



There is one more thing to be especially noticed in the act of walking. In- 

 asmuch as the body is being constantly supported and balanced on each leg 

 alternately, and therefore on only one at the same moment, it is evident that 

 there must be some provision made for throwing the center of gravity over the 



