FOOT AND FOREARM AS LEVERS 67 



its piston cord. The humerus has become a lever of 

 the third order ; its fulcrum is at the elbow ; the weight 

 of the body is attached to it at the shoulder and repre- 

 sents the load which has to be lifted. We also notice 

 that the brachial muscle is attached a long way up the 

 humerus, thus increasing its power very greatly, although 



ANCH 



ANTERIOR BRACHIAL 

 'powerj 



, BODY 

 (weight) 



Fig. 18. ■ 



HUMERUS 



(Lever) 



, ELBOW . 

 (Fulcrum) 



-Showing the action of the brachialis anticus in the arm 

 of an anthropoid ape. 



the rate at which it helps in lifting the body is diminished. 

 We can see, then, why the humerus is short and the fore- 

 arm long in anthropoid apes ; shortening the humerus 

 makes it more powerful as a lever for lifting the body. 

 That is why anthropoids are strong and agile tree-climbers. 

 But then watch them use those long hands and forearms 

 for the varied and precise movements we have to perform 

 in our daily lives, and you will see how clumsy they are. 



