OHAPTEK L 



FUNCTIONS OF THE CEREBRUM 



THE cerebrum is the seat of those psychical or mental processes 

 which are called volition and feeling ; volition is the starting-point 

 in motor activity; feeling or consciousness is the final phase of 

 sensory impressions ; the correlation of sensations with one another, 

 and with volitional impulses so generated is what constitutes 

 thought. That the brain is the organ (or anatomical correlate) of 

 mind is to-day a matter of such common knowledge that it is 

 almost superfluous to mention it in a physiological text-book. Yet 

 its functions were entirely unknown or only dimly conjectured by 

 ancient philosophers, and the overwhelming importance of the grey 

 matter on its surface in mental phenomena is a discovery of com- 

 paratively recent date. 



Effects of Removal of the Cerebrum. 



The functions of any organ may be discovered (in part, at any 

 rate) by removing it ; and the brainless frog which we have studied 

 in relation to the functions of the spinal cord is also a useful object- 

 lesson to teach us the uses of the part removed, by observing in 

 what manner the animal differs from one which has its brain intact. 

 If, instead of taking a frog, we take an animal lower in the scale, 

 where the brain is not so fully developed, the effect of removing that 

 organ will be less marked ; or if we remove the brain in a more 

 highly developed animal, the simultaneous removal of the brain 

 functions will be naturally more noticeable. We have already seen 

 (Chapter XLIV.) that the development of the cerebral hemispheres 

 increases in importance as we rise in the animal scale. 



If the cerebral hemispheres are removed in a teleostean or bony 

 fish (and in such animals there is only a rudimentary cortex), the 

 animal is to all intents and purposes unaffected ; it can distinguish 

 between a worm and a piece of string, and will rise to red wafers in 

 preference to those of another colour. The operation does not 



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