94 THE PRINXIPLES OF MVODYNAMICS. 



(8.) If the arm is rotated inward, the head of 

 the humerus will turn under the acromion, and 

 the arm can then be elevated so as to come 

 more directly upward. 



87. There are some points of dynamic import- 

 ance to add to the facts above stated : 



(i.) Let the elbow meet with a resisting sur- 

 face — acting as a powei^ — abducting the arm until 

 the great tuberosity of the humerus comes against 

 the acromion. Let the acromion be the weight 

 — then the resistance of the lower portion of the 

 capsule will represent the fulcrum — which may 

 practically give way and let the head of the 

 humerus out of the socket. The Jmmcrits, inider 

 the cirannstances, will be a lever of the second 

 ordei' — and, on account of the length of the 

 power-arm and on account of the comparative 

 shortness of the weight -arm, will apply great 

 force to the capsule. Also the prominent part 

 of the head of the humerus will be brought 

 nearer the lower border of the socket, and so be 

 more apt to slip off into the axilla. And the 

 adductors of the arm will be put on the stretch, 

 and will have their displacing components aug- 



