42 



HAND-BOOK OF PHYSIOLOGY. 



successive acts in taking the first step in walking are represented in Fig. 

 291, 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 for- 

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

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

 ward on the pelvis, especially the rectus femoris, with the psoas and the 

 iliacus; %ndly, the hamstring muscles, which slightly bend the leg on the 

 thigh; and Srdly, the muscles on the front of the leg, which raise the 

 front of the foot and toes, and so prevent the latter in swinging forward 

 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. 291). 



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 forward over the right leg, 

 now bearing nearly the whole weight, until it is time that in its turn 

 the left leg should swing forward, 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 front of the trunk and of the same leg (and of the other leg, except 

 when it is swinging forward) are helping the act by pulling the legs and 

 trunk, so as to make them incline forward, the rotation in the inclining for- 

 ward being effected mainly at the ankle joint. Two main kinds of lever- 

 age 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. 290. 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 repre- 

 sentation 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. 290), while the raising 

 of the heel and pushing forward of the trunk by the calf -muscles is roughly 

 represented 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 forward to support the trunk, which is at the same 

 time pushed and pulled forward by the muscles of the other, may be 

 gathered from the previous description. 



