148 THE HUMAN BOD 7. 



lion in which the muscles are commonly inserted into the* 

 bones, much of their force is lost so far as producing move- 

 ment is concerned. Suppose the log of wood in the dia- 

 gram (Fig. 60) to be raised by pulling on the rope in the 

 direction a; it is clear at first that the rope will act at a 

 great disadvantage; most of the pull transmitted by it will 

 be exerted against the pivot on which the log hinges, and 

 only a small fraction be available for elevating the latter. 

 But the more the log is lifted, as for example into the 

 position indicated by the dotted line, the more useful will 

 be the direction of the pull, and the more of it will be spent 

 on the log and the less lost unavailingly in merely increas- 

 ing the pressure at the hinge. If we now consider the ac- 

 tion of the biceps (Fig. 49) in flexing the elbow-joint, we 

 see similarly that the straighter the joint is, the more of 



FIG. 60. Diagram illustrating the disadvantage of an oblique pull. 



the pull of the muscle is wasted. Beginning with the arm 

 straight, it works at a great disadvantage, but as the fore- 

 arm is raised the conditions become more and more favor- 

 able to the muscle. Those who have practiced the gym- 

 nastic feat of raising one's self by bending the elbows when 

 hanging by the hands from a horizontal bar, know practi- 

 cally that if the elbow-joints are quite straight it is very 

 hard to start; and that, on the other hand, if they are kept 

 a little flexed at the beginning the effort needed is much 



