CHAPTER IX 

 THE BRAIN (Continued) THE CEREBRUM 



The importance of the cerebrum to the capacities 

 of animals for reaction varies within the widest limits. 

 We shall find that in ourselves it is without question 

 the supreme division of the brain. As we descend in 

 the scale of vertebrate life its place is less and less im- 

 pressive until in the fish it serves chiefly to connect the 

 organs of smell with the brain-stem. This seems a 

 trifling function but it is one which the cerebrum in 

 all cases fulfils. The cerebrum cannot be removed for 

 purposes of experiment without isolating and rendering 

 useless the receptors of the nose. (We have seen 

 already that none of the cranial nerves beside the ol- 

 factory connect directly with the cerebrum.) 



Decerebrate Animals. An animal from which the 

 cerebrum has been removed is termed decerebrate. 

 From its behavior we can arrive at conclusions regard- 

 ing the extent to which the cerebrum figures in the 

 life-processes of any particular species. The operation 

 is a simple one in the cold-blooded types but becomes 

 increasingly difficult in the higher forms. It has been 

 successfully performed upon birds and even dogs. 



Fish are but little affected by the loss of this part of 

 the brain. They are reported to behave so nearly like 

 their mates that it is not possible to identify the de- 

 cerebrate fishes among normal ones in an aquarium. 

 They show the same preferences for certain foods that 

 were demonstrated before the trial. A few kinds of 

 fish among them, sharks are said to become notably 

 inert, but close observation has shown that this is owing 

 to the loss of the olfactory organs on which they evi- 

 dently depend to an exceptional degree. 



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