MOTION. 



are too intimately associated with, the function of " Diges- 

 tion," to be described apart from it. There are, however, 

 one or two very important and somewhat complicated mus- 

 cular acts which may be best described in this place. 



Walking. In the act of walking, almost every voluntary 

 muscle in the body is brought into play, either directly 

 for purposes of progression, or indirectly for the proper 

 balancing of the head and trunk. The muscles of the- 

 arms are least concerned ; but even these are for the most 

 part instinctively in action also 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 (fig. 166). When starting to walk, 

 Fig. 1 66. 



123 45 



say with the left leg, this raising of the body is not left 

 entirely to 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 con- 

 traction, 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 walking are represented in fig. 166, I, 2, 3. 



