THE BRAIN 129 



plotted in little areas concerned with specific functions 

 gave way for a time to the view that there is no distinction 

 between the duties of its different parts. It was com- 

 pared with the liver, a large organ having several simul- 

 taneous activities. A particular lobe of the liver is not 

 supposed to have a single service but rather to participate 

 in all the work of the organ as a whole. So it came to be 

 thought of the brain that cerebral functions are not 

 local but diffuse. To destroy a part, it was held, would 

 not suppress any one power but would weaken all. 



When new evidence of localization in the cerebrum 

 began to be obtained the emphasis was quite different 

 from that which had prevailed in the days of phrenology. 

 Less was said of the correlation of brain and mind and 

 more of the correlation of brain and body. The first 

 special areas to be defined were those which we call 

 motor, regions of the cortex which appear to have a 

 closer connection with the skeletal muscles than can be 

 claimed for other portions. 



The Motor Areas. These are distinguished by the 

 fact that electric stimulation applied anywhere within 

 their boundaries causes movements of various parts of 

 the body. The muscular responses occur chiefly on the 

 opposite side as already implied. The motor areas 

 have been carefully mapped for the cat, the dog, and the 

 ape. In the last-named animal the general appearance 

 of the brain is very like the human and there is no doubt 

 that in the cerebrum of man there are motor areas in a 

 corresponding position. A diagram will show how they 

 are placed. Cerebral localities are referred to under the 

 names of the bones of the skull which lie over them and 

 these areas are said to be in the frontal region along the 

 border of the parietal. Roughly, they may be said to 

 extend upward from the ear to the top of the head. 



Microscopic study of the brain shows that the surface 



gray matter of the motor regions contains many large 



nerve cells, of a type called pyramidal, from which the 



axons of nerve cells pass inward. The fibers which 



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