66 THE ENGINES OE THE HUMAN BODY 



find that the labouring peoples of the world — Europeans 

 and Mongolians — have usually short forearms and hands, 

 while the peoples who live on such bounties as Nature 

 may provide for them have relatively long forearms 

 and hands. 



Now, man differs from anthropoid apes, which are 

 distant cousins of his, in having a forearm which is 

 considerably shorter than the upper arm ; whereas in 

 anthropoid apes the forearm is much the longer. That 

 fact surprises us at first, especially when we remember that 

 anthropoids spend most of their lives amongst trees and 



ANTERIOR BRACHIAL 



/ • *.\ ANTERIOR BRACHI' 



[WeighCJ MUSCLE (Power 



HUMERUS 



HAND ULNA ELBOVS 



(Fulcrum ) 



Fig. 17B. — The forearm and hand as a lever of the third order. 



use their arms much more than their legs in swinging the 

 weight of their heavy bodies from branch to branch and 

 from tree to tree. A long forearm and hand give them a 

 long and quick reach, so that they can seize distant branches 

 and swing themselves along safely and at a good pace. 

 Our first thought is to suppose that a long forearm, 

 being a weak lever, will be ill adapted for climbing. But 

 when you look at fig. 18, the explanation becomes plain. 

 When a branch is seized by the hand, and the whole weight 

 of the body is supported from it, the entire machinery of 

 the arm changes its action. The forearm is no longer 

 the lever which the brachial muscle moves (fig. 18), but 

 now becomes the base from which it acts. The part which 

 was its piston cord now serves as its base of fixation, and 

 what was its base of fixation to the humerus becomes 



