LIVING IN OUR ENVIRONMENT 



35 



some large, some small, that go into this work of moving 

 the hand and wrist. The muscles are attached to bones 

 by means of cords called tendons. You can feel these 

 cords in your wrist and you may have 

 found that movement of the fingers is 

 controlled by them. Study of the 

 figure will show that these tendons are 

 attached to muscles of the forearm so 

 that movement of the hand is controlled 

 by them. But we have again only 

 begun to find the adaptations in the 

 hand. All of the muscles must act 

 together and must be directed by 

 means of our nervous system. They 

 must be supplied with blood contain- 

 ing food and oxygen (see page 376) if 

 they are to do work. The skin must study this care f u iiy 

 be sensitive so we may know when we and then explain how 

 touch anything. If we see the thing 

 we touch, the eye plays a part. And 

 now that we have mentioned all of these structures, we 

 do not begin to understand how each part acts in grasping 

 the pencil, let alone how we make the complicated and 

 delicate actions which occur when we write our names. 



The human body is full of adaptations, most of which 

 are far more wonderful than those just described. To 

 understand them thoroughly we must study physiology, 

 a subject to be taken up in the senior high school. But 

 we can see that the human body is a very complicated 

 machine and that our job in life is to learn to run it effi- 

 ciently. 



Adaptations May Be Acts as Well as Structures. But 

 animals often have ways of doing things which are adap- 

 tations. Certain tropical ants, for example, cut leaves 

 from trees, carry the pieces to their nests, and there use 



you 



can move your 

 fingers. 



