THE BRAIN 



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the left, separated by a very deep fissure. It is composed of a 

 thick layer of grey matter surrounding white fibrous nerve-sub- 

 stance. The grey matter is drawn up into a number of folds or 

 convolutions, by which its surface is greatly increased ; and as the 

 pia mater (which, it will be remembered, is the source from which 

 the substance of the brain is supplied yith blood) dips into all the 

 fissures between these folds, we lave reason to believe that the 

 use of this arrangement is to provide the brain with a plentiful 



Fig. 1 66. The TJpper Surface of the Cerebrum, showing its division into 

 two Hemispheres, and also the Convolutions. 



supply of blood. The other coats of the brain the arachnoid 

 and the dura mater do not dip into the fissures of the grey 

 matter, but pass straight across them. 



The functions of the cerebrum. The cerebrum is the chief 

 seat of sensation, intelligence, the will, and the emotions. When 

 we examine the brains of various animals, we notice that the size 

 of the cerebral hemispheres and the complexity of the convolutions 

 are proportional to the intelligence of the animal. Thus, in the 



