ADJUNCTS OF THE MUSCULAR SYSTEM. 107 



of the two legs is alternately thrown forward by an oscilla- 

 tory movement exactly similar to that of a pendulum. 



Let us suppose a man stopped in the act of walking : he 

 has just completed one step, and stands upon his two legs, 

 the left, for instance, being placed before, and the right be- 

 hind. To continue his walk, to make a new step, what hap- 

 pens is as follows : the left leg, which we will call the active 

 leg, is placed perpendicularly upon the ground, and forms the 

 right side of a rectangular triangle, of which the hypothe- 

 nuse is formed by the right leg, stretched out behind ; the 

 right leg, we shall see, may be called the passive leg. The 

 left or active leg, at first slightly bent, is then extended, and 

 carries the pelvis forward and upward. To produce this 

 effect the heel of the left foot is raised from the ground by 

 means of the mechanism which we explained a propos of 

 levers of the second kind, and the limb now leans only upon 

 the extremity of the metatarsus. During this movement 

 the right or passive leg, being forced to follow the forward 

 movement of the pelvis, is passively detached from the 

 ground, and makes a forward movement, like a pendulum, 

 around its point of suspension to the pelvis, by which the 

 right foot is carried as far before the active foot (the left) as 

 it was previously behind it; it is then placed upon the 

 ground, and the movement, by which the active leg (the left) 

 throws forward the pelvis, being continued and finished, the 

 right foot finds itself at last placed perpendicularly upon the 

 ground, as was the left foot at the beginning of the step. 

 The step which we have been considering is finished, and in 

 the new one which follows the same takes place, the parts 

 only being reversed : the right leg becomes the active one, 

 the left the passive. 



In short, the walking step may be represented by a rec- 

 tangular triangle which changes its position, the sides mov- 

 ing in such a manner that the one which represented the 

 right side at the beginning of the step (the left leg in the 

 preceding example) passes into the position of the hypoth- 

 enuse, and vice versa. The leg which, from the right side, 

 passes into this position is all the time active, while the leg 

 which passes from the position of hypothenuse into that of 

 the right side is all the time passive, and oscillates in the 

 same manner as a pendulum. In order to oscillate without 

 touching the ground, the passive leg must be slightly short- 

 ened; this takes place without any aid from the muscles of 





