470 MOTION. 



such a way that it would fall prostrate were it Dot that the 

 right foot is brought forward and planted on the ground to 

 support it. Thus the muscles of the left calf are assisted in 

 their action by those muscles on the front of the trunk and 

 legs which, by their contraction, pull the body forwards ; and 

 of course, if the trunk form a slanting line, with the inclina- 



FlG. 166. 



tion forwards, it is plain that when the heel is raised by the 

 calf-muscles, the whole body will be raised, and pushed ob- 

 liquely forwards and upwards. The successive acts in taking 

 the first step in walking are represented in Fig. 166, 1, 2, 3. 



Now it is evident that by the time the body has assumed 

 the position No. 3, it is time that the right leg should be 

 brought forward to support it and prevent it from falling pros- 

 trate. This advance of the other leg (in this case the righfy 

 is effected partly by its mechanically swinging forwards, pen- 

 dulum-wise, and partly by muscular action ; the muscles used 

 being, 1st, those on the front of the thigh, which bend the 

 thigh forwards on the pelvis, especially the rectus femoris, with 

 the psoas and the iliacus ; 2dly, the hamstring muscles, which 

 slightly bend the leg on the thigh ; and 3dly, the muscles on 

 the front of the leg, which raise the front of the foot and toes, 

 and so prevent the latter in swinging forwards from hitching 

 in the ground. Anybody who has attentively watched the 

 helpless flapping action of the foot and leg in cases of partial 

 paralysis affecting the muscles of the leg, or who will, in his 

 own case, note the act of bringing the leg forward in walking, 

 will be convinced of the large share which the muscles take 

 in the act in question ; although, of course, their work is ren- 

 dered much easier by the pendulum-like swinging forward of 

 the leg by its own weight. 



The second part of the act of walking, which has been just 

 described, is shown in the diagram (4, Fig. 166). 



When the right foot has reached the ground the action of 



