A STUDY OF THE NERVOUS SYSTEM 



281 



Rolando are the nerve cells that control the movements 

 of the arms and legs. If the right half of the brain in 

 this region be injured, paralysis on the left side of the 

 body is likely to follow. From facts like these we know 

 that the nerve trunks, after leaving the motor cells, cross 

 the brain and 

 spinal cord, and 

 supply the op- 

 posite side of the 

 body. This is 

 true of nearly all 

 the nerve trunks. 

 A right-handed 

 man is there- 

 fore left-brained. 

 One should, how- 

 ever, guard 

 against the idea 

 that the brain 

 can be divided 

 into different re- FlG ' 129 '~ side View of Brain, showing Localiza- 

 tion of Functions, 

 gions that work 



independently. An injury to a single region of the brain 

 often destroys, for a time at least, all consciousness and 

 all power of motion. This is often the result of a blow 

 on the head. 



Habitual Activities Can you remember the time when 

 you learned to write? If so, you will recall that each 

 letter was traced laboriously by a conscious effort of your 

 brain to guide the muscles of your fingers. Writing, in 

 our early years, belonged to the group of our conscious 

 activities. But as time went on, less and less of our 

 attention was needed for this mechanical process, until 

 now our fingers seem to move of themselves. Walking, 

 bicycle riding, swimming, playing the piano, putting on 

 our clothes, conveying the food to our mouths none of 



