NORMAL AND ABNORMAL MOVEMENTS. 109 



notice that the heel of the passive leg in swinging forwards in its 

 cycloid-like descent does not immediately strike the ground, but 

 that just previous to the impact it again makes a slight ascent. 

 This is shown not only in the curve, but also in all of the plates 

 illustrating the normal walk. (See, also. Fig. 5.) We should ob- 

 serve at the same time that the rate of motion is not by any means 

 uniform. It is relatively slow in the beginning, but steadily in- 

 creases in velocity until the step is almost completed, when a slow- 

 ing of movement again takes place. This slowing of movement 

 is coincident with the secondary rise. The impact of the heel upon 

 the ground is then made without any waste of force and with a 

 minimum amount of jar. When in addition we reflect that the 

 heel is but a portion of a moving lever and that the muscles at- 

 tached to this lever are elastic, we realize that the jar of impact 

 is indeed reduced to a minimum. 



The curves of the lateral sway are also exceedingly interest- 

 ing. The fact that the lateral sway of the head is greater than 

 that of the hip is exactly in keeping with what we should expect 

 on a priori grounds. The pelvis is relatively fixed and not nearly 

 so free to move as the head or upper portions of the trunk, and, 

 secondly, the tilting of a column is. naturally exaggerated at its 

 upper and free end. 



The lateral sway of the foot again presents an interesting inter- 

 pretation. Its extent is less than most of us would have expected 

 to find, being in fact very small. This signifies undoubtedly that 

 the extent of the lateral sway is, other things equal, always the 

 least possible consistent with the working of the limb ; because, 

 first, the greater the lateral sway the greater the loss of time con- 

 sumed in again bringing the foot to the ground ; and, secondly, the 

 greater the lateral sway of the foot the greater the lateral sway of 

 the body as a whole, and the greater the loss of time and force at 

 the expense of the forward movement. 



Finally, taking all of the trajectories together, it is evident that 

 the movements in the three directions, forward, vertically, and later- 

 ally, are correlated. Secondly, the prime object of the walk being 

 movement in a forward direction, it follows, other things equal, 

 that the greatest economy of time and force obtains when the 

 vertical and lateral movements are reduced to a minimum. This 

 is apparently the case in the normal walk. 



