148 THE HUMAN BODY. 



cation of the power. In the Body the power-arm is usually 

 very short so as to gain speed arid range of movement, the 

 muscles being powerful enough to still do their work in spite 

 of the mechanical disadvantage at which they are then placed. 

 The limbs are thus made much more shapely than would be 

 the case were the power applied near or beyond the weight. 



It is of course only rarely that simple movements as those 

 described above take place. In the great majority of those 

 executed several or many muscles co-operate. 



The Loss to the Muscles from the Direction of their Pull. 

 It is worthy of note that, owing to the oblique direction in 

 which the muscles are commonly inserted into the bones, 

 much of their force is lost so far as producing movement is 

 concerned. Suppose the log of wotid in the diagram (Fig. 

 67) 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 

 lines, 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 unavail- 

 ingly in merely increasing the pressure at the hinge. If we 

 now consider the action of the biceps (Fig. 52) in flexing the 

 elbow-joint, we see similarly that the straighter the joint is, 

 the more of the pull of the muscle is wasted. Beginning 



FIG. 67. Diagram illustrating the disadvantage of an oblique pull. 



with the arm straight, it works at a great disadvantage, but 

 as the forearm is raised the conditions become more and more 



