THE MUSCULAR SYSTEM. 425 



the same way that the pole might be by the force applied at p. (Fig. 

 298), 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 bar- 

 row. The manner 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 timepushed and pulled forwards by the mus- 

 cles of the other, may be gathered from the previous description. 



There is one more thing to be noticed especially in the act of walk- 

 ing. Inasmuch 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 

 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 way, and the manner in which it is effected is one ele- 



Fio. 300. 



ment in the differences 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 grav- 

 ity 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. 299, 3, the pelvis is instinctively by various muscles, 

 made to rotate on the head of the left femur at the acetabulum, to the 

 left side, so that the weight may fall over the line of support formed by 

 the left leg at the time that the right leg is swinging forwards, and leav- 

 ing all the work of support to fall on its fellow. Such a "rocking" 

 movement of the trunk and pelvis, however, is accompanied by a move- 

 ment of the whole trunk and leg over the foot which is being planted on 

 the ground (Fig. 300); the action being accompanied with a compensa- 

 tory outward movement at the hip, more easily appreciated by looking 

 at the figure (in which this movement is shown exaggerated) than de- 

 scribed. 



