MOVEMENTS.] 



PHYSIOLOGY, 



33 



white nerve-trunks as they are called, which we should 

 find passed at last between the vertebrae, somewhere 

 in the neck, into the inside of the vertebral canal, 

 where they became mixed up with the mass of nervous 

 material we have already spoken of as the spinal cord. 



What ha\ e these nerves to do with the bending of 

 the arm ? Why simply this. Suppose you were able 

 without much trouble to cut across the delicate 

 nerves going to your biceps, and did so : what would 

 happen? You would find that you had lost all 

 , power of bending your arm; however much you 

 willed it, there would be no swelling rise up in 

 your arm. Your biceps would remain perfectly quiet, 

 and would not shorten at all, would not contract in 

 obedience to your will. ♦ 



What does this show? I*: proves that when you 

 will to bend your arm, something passes along the 

 nerves going to the biceps muscle, which something 

 causes that musclp to contract? The nerve, then, is 

 a bridge between your will and the muscle — so that 

 when the bridge is broken or cut away, the will 

 cannot gef to the muscle. 



If anywhere between the muscle and the spinal 

 cord you cut the nerve which goes, or branches from 

 which go, to the muscle, you destroy the communica- 

 tion between the will an ! the muscle. 



The spinal cord, as we have seen, is a mass of 

 nervous substance continuous with the brain; from 

 the spinal cord nearly all the nerves of the body are 

 given off ; those nerves whose branches go to the 

 , biceps muscle in the arm leave the spinal cord some- 

 where in the neck. 



If you had the misfortune to have your spinal 



