600 MOTION. 



them incline forward, the rotation in the inclining forwards 

 being effected 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 detail will be under- 

 stood with comparative ease. One kind of leverage 

 employed in walking is essentially the same with that 

 employed in pulling forward the pole, as in fig. 165. 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 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, (fig. 165) while the raising of the heel and pushing 

 forwards of the trunk by the calf-muscles is roughly repre- 

 sented 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 forwards to sup- 

 port the trunk, which is at the same time pushed and pulled 

 forwards by the muscles of the other, may be gathered 

 from the previous description. 



There is one more thing to be noticed especially in 

 the act of walking. Inasmuch as the body is being con- 

 stantly 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 

 centre of gravity over the line of support formed by the 

 bones of each leg, as, in its turn, it supports the weight 

 of the body. This may be done in various ways, and the 

 manner in which it is effected is one element in the dif- 

 ferences which exist in the walking of different people. 

 Thus it may be done by an instinctive slight rotation of 

 the pelvis on the head of each femur in turn, in such a 

 manner that the centre of gravity of the body shall fall 

 over the foot of this side. Thus when the body is pushed 



