THE STORY OF THE BRAIN AND NERVE 119 



cerebrum is seen to be divided lengthwise into two 

 halves or lobes (Fig. 32), the division extending to a 

 short depth between the lobes, where they are found 

 to be connected together by a bridge of nervous 

 matter known as the corpus callosum. The surface 

 of a man's brain is thrown into a series of distinctly 

 marked folds or convolutions (Fig. 34). These con- 

 volutions are characteristic of many other animals, 



PO.F 



Fig. 34. SIDE VIEW OF BRAIN REGIONS 



AND CONVOLUTIONS. 



The shaded part corresponds to the motor area. The 



left lobe of the brain is represented here, the front or 



forehead region lying to the left side. 



but are absent in the brains of certain forms, of which 

 the beaver, rabbit, and the like animals are examples. 

 The convolutions do not vary in one individual from 

 those of another that is to say they form a definite 

 pattern, presenting occasionally variations, but still 

 maintaining a close anatomical similarity and re- 

 semblance. For scientific and medical purposes the 

 convolutions are all duly marked and numbered. 

 The surface of the brain has similarly been divided 

 into certain areas or regions corresponding with the 



