Inclination of the Scapulum to the Horizontal. 



Position o 47° 



" I 54° 



2 64° 



'■ 3 70° 



" 4 73° 



while the humerus is closing its angle during the first four 



positions. This angle is as follows : 



Inclination of the Humerus to the Horizontal. 



Position o 86° 



" I 76° 



" 2 56° 



" 3 48° 



At position 4, when the foot leaves the ground the 

 humerus quickly comes back toward the vertical, forming 

 an angle of 57° with the horizontal. 



Thus, so far as the shoulder and arm are concerned, 

 the work of shock absorption and of compression of the 

 spring which is to produce the period of suspension is 

 characterized by approach to verticality on the -part of 

 the shoulder and by approach to horizontality on the part 

 of the arm and this double movement in opposite angular 

 directions continues until the critical movement when, 

 equilibrium being about to be lost and the foot about to 

 leave the ground, the arm rotates suddenly downward 

 and causes projection through the air. 



If, in figure 3, we project to the points a and b on X Y, 

 the points A and B, respectively the upper end of the 

 shoulder and the lower end of the arm in position 3, we 

 see that the critical moment when equilibrium is about to 

 be disturbed is when the distance separating the two pro- 

 jections is greater than a b (a having passed b in the for- 

 ward direction as shown in figure 3). 



19 



