MUSCULAR AND SKELETAL SYSTEMS. 



229 



Or take the case of the deltoid holding a weight at 

 arm's length (Fig. 147). I suppose a man of good mus- 

 cular vigor will hold at arm's length a weight of thirty 



Fig. 147.— Diagram showing the power of the deltoid in raising ,-y) 

 the arm. ' ' 



gastr 



pounds. Now, in order to do so, the deltoid taking hold 

 at four inches from the fulcrum, /, and the weight held 

 at two feet from the same, if it pulled directly upward it 

 would have to pull with a force of 30 x 6 = 180 pounds. 

 But it pulls at a small angle, and we must 

 multiply this again by at least four — i. e., 

 180 X 4 = 720 pounds. 



Or take one more — viz., the case of the 



rocnemius and soleus muscles (the calf 



the leg) lifting the heel. I suppose any 



son of ordinary weight and vigor can 



e another person of average weight, 



one hundred and fifty pounds, on his 



back, making altogether, say, three hundred 



nds, and, standing on one foot, rise to 



oe. Let us see what the strain on the 



tendo-Achillis is in doing so. 



Taking the distance from the 



fulcrum (2, Fig. 148) to the 



insertion of the tendon, 1, as 



one inch, and the distance 



from the same to the ball of 



the toes, J, as six inches, then we have the proportion 1, 2 



= one inch : 2, j = 6 inches : : 300 pounds : x, and x — 



1,800 pounds. Or if some one objects (as has been often 



Fig. 148. — Diagram showing the 

 power of the gastrocnemius and 

 soleus muscles in tiptoeing. 



