114 THE PRINCIPLES OF MYODYNAMICS. 



tibia the movable bone — or the tibia the fixed 

 bone and the femur the movable bone. The 

 muscles that span both the knee-joint and the 

 hip-joint may make the femur the fixed bone 

 and the tibia and the pelvis the movable bones. 



107. See Fig. 24 : Pa is the patella ; q-e is 

 the quadriceps extensor ; Fe is the femur ; an3 

 T is the tibia : Draw the line W'P-D F hav- 

 ing a right angle at P and D : P is at the 

 insertion of the tendo-patellse, and F is where 

 the tibia and femur come in contact. The dis- 

 tance P D is about two inches, and the length of 

 the tibia is about fourteen inches : and W D P 

 is a bent lever of the first order, whose fulcrum 

 is D F. Let the lower end of the femur rest on 

 a resisting surface, and let a weight of fifty 

 pounds be placed on the low^er end of the tibia 

 — always acting in the direction P D of the 

 power-arm of the lever. By the principles of 

 the lever : 



2 X P — 14 x 5o . (i.) 

 Hence, P = 35o . . . (2.) 

 But, F = P -f W = 400 . (3.) 



Therefore, the pull of the quadriceps equals 



