LOCOMOTION 



477 



least concerned; but even these are for the most part instinctively in action 

 to some extent. 



Among the chief muscles engaged directly in the act of walking are those of 

 the calf, which, by pulling up the heel, pull up also the astragalus, and with it, 

 of course, the whole body, the weight of which is transmitted through the 

 tibia to this bone, figure 340. When starting to walk, say with the left leg, 

 this raising of the body is not entirely dependent on the muscles of the left 

 calf, but the trunk is thrown forward in such a way that it would fall prostrate 

 were it not 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 forward; and, of course, if the trunk form a slanting line, with 

 the inclination forward, it is plain that when the heel is raised by the calf 

 muscles, the whole body will be raised, and pushed obliquely forward and 



FIG. 340. 



upward. The successive acts in taking the first step in walking are repre- 

 sented in figure 340, i, 2, 3, etc. 



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 right leg is effected 

 partly by its mechanically swinging forward, pendulum- wise, and partly by 

 muscular action; the muscles used being i, 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; 2, the hamstring muscles, which slightly bend 

 the leg on the thigh; and, 3, 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 striking the ground. 



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

 shown in the diagram, 4, figure 340. 



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 the time when the left leg should again swing forward, 

 and the left foot be planted on the ground to prevent the body from falling 



