424 HANDBOOK OF PHYSIOLOGY. 



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

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

 wards and upwards. The successive acts in taking the first step in walk- 

 ing are represented in Fig. 299, 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 prostrate. This advance of the other leg 

 (in this case the right) is effected partly by its mechanically swinging 

 forwards, pendulum-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; 2dty, the hamstring muscles, which slightly bend the leg 

 on the thigh; and 3f%, 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. 



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

 is shown in the diagram (4, Fig. 299). 



When the right foot has reached the ground the action of the left 

 leg has not ceased. The calf-muscles of the latter continue 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 mus- 

 cles on the front 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 mam 

 kinds of leverage are, therefore, employed in the act of walking, and if 

 this idea be firmly grasped, the details will be understood with compara- 

 tive ease. On kind of leverage employed in walking is essentially the 

 same with that employed in pulling forward ^the pole, as in Fig. 298. 

 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 alto- 

 gether bad lepresentation of the two main levers employed in the act of 

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



