602 MOTION. 



onwards and upwards by the raising, say, of the right heel, 

 as in fig. 159, 3, the pelvis is instinctively, by various 

 muscles, made to rotate on the head of the left femur at 

 Fig. 1 60. the acetabulum, to 



the left side, so that 

 the weight may fall 

 over the line of sup- 

 port formed by the 

 left leg at the time 

 that the right leg is 

 swinging forwards, 

 and leaving all the 

 work of support to 

 fall on its fellow. 

 Such a ' rocking ' 

 movement of the 

 trunk and pelvis, 

 however, is but an 

 awkward manner of 

 doing what can be 

 done more gracefully by combining a slight * rocking ' with 

 a movement of the whole trunk and leg over the foot which 

 is being planted on the ground (fig. 1 60) ; the action being 

 accompanied with a compensatory outward movement at 

 the hip, more easily appreciated by looking at the figure 

 (160) than described. 



Thus the body in walking is continually rising and 

 swaying alternately from one side to the other, as its cen- 

 tre of gravity has to be brought alternately over one or 

 other leg ; and the curvatures of the spine are altered in 

 correspondence with the varying position of the weight 

 which it has to support. The extent to which the body is 

 raised or swayed differs much in different people. 



In walking, one foot or the other is always on the ground. 

 The act of leaping, or jumping, consists in so sudden a 

 raising of the heels by the sharp and strong contraction of 



