SECTION XVII 



THE FUNCTIONS OF THE CEREBRAL 

 HEMISPHERES 



IN an animal possessing cerebral hemispheres it is impossible to 

 foretell with certainty what particular reaction may be evoked by 

 any stimulus. The animal which has been deprived of its hemi- 

 spheres can, as we have seen, be played on at will, whereas the intact 

 animal is an individual whose actions to judge by our own experience 

 are guided by intelligence, and influenced by motives or by feelings 

 of fear, hunger, pain, and the like. In short, its behaviour is analogous 

 to that which in man we associate with conscious feeling and volition. 

 This association of the volitional manifestations with the cerebral 

 hemispheres has long been assumed, and is borne out by the exact 

 parallelism existing between the degree of intelligence with which an 

 animal is endowed and the extent of development of its cerebral 

 hemispheres. Moreover in man himself there is a proportionality 

 between the average size of the brain, i.e. of the cerebral hemispheres, 

 and the average intelligence of the race. 



Earlier attempts to analyse the factors entering into the sphere of 

 consciousness and to associate with these factors localised parts of the 

 brain failed, largely on account of a faulty psychological analysis and 

 the absence of any proper experimental groundwork for the conclusions 

 put forward. Gall, the founder of phrenology, recognised more 

 clearly than previous authors that the cerebral hemispheres must be 

 regarded as the material basis of consciousness. Impressed, however, 

 by the fact that there was no proportionality between the acuteness 

 of the senses and the degree of development of the cerebral hemispheres, 

 he considered that any division of functions among different parts 

 of the hemispheres must relate to highly complex psychical conditions, 

 and therefore on very slender grounds allotted to parts of the brain 

 functions such as those of intelligence, memory, judgment, amativeness, 

 and so on. These conclusions of Gall were overthrown by Flour ens 

 on both theoretical and experimental grounds. In the first place, 

 Flourens pointed out that the mental faculty of man cannot be divided 

 up into a number of different independent qualities or faculties, such 

 as those proposed by Gall. In the second place, he showed that in 

 the pigeon, although loss of the whole cerebral hemispheres destroyed 



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