MUSCLE-NERVE PHYSIOLOGY. 



525 



the whole body will be raised, and pushed obliquely forward and upward. 

 The successive acts in taking the first step in walking are represented in 

 fig 337, 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 pre- 

 vent it from falling prostrate. This advance of the other leg (in this case the 

 right) is effected partly by its mechanically swinging forward, pendulum- 

 wise, and partly by muscular action ; the muscles used being 1st , those on the 

 front of the thigh, which bend the thigh forward 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 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. 337). 



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 u^ 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 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 forward 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 details will be understood with com- 

 parative ease. One kind of leverage employed in walking is essentially the 

 same with that employed in pulling forward the pole, as in fig. 336. 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 representation 

 of the two main levers employed in the act of walking. The body is putted 

 forward by the muscles in front, much in the same way that the pole might be 

 by the force applied at P., 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 Dy the muscles 

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



