THE PRINCIPLES OF MYODYNAiMICS. g5 



mented, which may be looked upon as so much 

 weight to be added to the resistance of the acro- 

 mion, and thus the displacement of the head of 

 the humerus into the axilla will be doubly 

 assured — on the principle of a lever of the 

 second order. — 



(2.) But, if the displacing components of the 

 adductors and the resistance of the acromion be 

 looked upon as the power, the principle of a 

 lever of the third order will be involved, and the 

 fulcrum will be overcome : — which is the lower 

 and internal portion of the capsular ligament. 



88. The following problem may now be 

 solved : — To determine, in a given case, the strain 

 on the inner and lower portion of the capside of 

 the shoidder -joint. — It will be convenient at 

 present to consider the humerus a lever of the 

 first order. — 



(i.) Let the power-arm of the lever be ten 

 inches long — -the distance from the elbow-joint to 

 the acromion. Let the weight-arm of the lever 

 be two inches long — the distance from the inner 

 and lower portion of the capsule to the acro- 

 mion. 



