THE PRINCIPLES OF MYODYNAMICS. 



I 2 I 



angle, the semi-tendinosus has a greater moving 

 component than the semi-membranosus, because 

 it acts on a longer power-arm : See Fig. 2 5. 

 Hence, during the first part of flexion of the 

 leg, the semi-membranosus is the more powerful 

 agent ; and during the second part of flexion of 

 the leg, the semi-tendinosus is the more power- 

 ful agent. — In these instances the tibia becomes 

 a lever of the third order. When the leg is 

 extended, the moving components are retentive : 

 but when the leg is semiflexed, the moving 

 components are displacing. 



113. a. In a given case the following meas- 

 urements were made : — 



(i.) From the center of rotation of the leg 

 about the internal condyle (which is the fulcrum) 

 outward to a point in a line drawn directly 

 upward from the insertion of the biceps cruris, 

 the distance was about two and one-half inches : 

 This would constitute the power-arm of a lever, 

 whose power is the biceps cruris. 



(2.) From the same center of rotation inward 

 to a point in a line drawn directly upward from 



