108 



A STUDY OF SOME 



definite point. It is seen at a glance that this curve is made up 

 of a number of elements. The curve from Y to S is formed by 

 the maleolus sweeping upward on an arc the radius of which 

 centres in the ball of the great toe. At the next instant ihe 

 centre of rotation is transferred to the tij) of the great toe, and 

 a change in direction is noticed, therefore, at the point S. The 

 balance of the curve up to the point Z is the result of the flex- 

 ion of the leg and of the forward movement of the pelvis ; thence 



Fig. 4. 



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Tracing and trajectory constructed from Plate 8. The trajectory is 

 supposed to pass through the external malleolus. (Incomplete.) 



to the final impact of the heel upon the ground the curve is the 

 resultant of a complex movement, in which three principal ele- 

 ments are distinguishable: first, a pen- 

 dulum movement, second, a fall, and 

 third, a forward movement, the latter 

 being due to the movement forward 

 of the body as a whole. The first two 

 elements are those of a cycloid, and 

 the foot therefore falls to the ground, 

 other things equal, along the line of 

 swiftest descent. 



A fourth element is observed in the 

 slight secondary ri.se occurring in the curve just previous to its 

 termination. The significance of this rise is as follows. We 



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Left foot, Plate 8. 



