WALKING. 471 



the left leg has not ceased. The calf-muscles of the latter con- 

 tinue to act, and by pulling up the heel, throw the body still 

 more forwards over the right leg, now bearing nearly the whole 

 weight, until it is time that in its turn the left leg should swing 

 forwards, and the left foot be planted on the ground to prevent 

 the body from falling 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/r0?^of the trunk and of the same leg (and 

 of the other leg, except when it is swinging forwards) are 

 helping the act by pulling the legs and trunk, so as to make 

 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 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 Fig. 165. And the other, less exactly, is that 

 employed in raising the handles of a wheelbarrow. Now, sup- 

 posing 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 

 represented on raising the handles of the barrow. The man- 

 ner in which these actions are performed alternately by each 

 leg, so that one after the other is swung forwards to support 

 the trunk, which is at the same time pushed and pulled for- 

 wards 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 constantly sup- 

 ported 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 differences which exist in the walking of differ- 

 ent people. Thus it may be done by an instinctive slight ro- 

 tation 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 onwards 

 and upwards by the raising, say, of the right heel, as in Fig. 



