FUNCTIONS OF THE NERVOUS SYSTEM 311 



453. Localization of Functions in the Cortex. The area 

 of the cortex, with all its convolutions, is in man about 

 four square feet. In the lowest vertebrate animals the 

 surface of the brain is smooth, but as animals rise in the 

 scale of intelligence fissures and folds appear, growing 

 more complex and more like those of man, till in the brain 

 of the highest apes a striking resemblance is seen to that 

 of man. 



The whole Surface of the human cortex has now been 

 mapped out into tracts, or districts, to many of which it is 

 found that special functions are assigned. Post-mortem 

 examination of diseased human brains, together with close 

 study of the effects of disease during life, and numer- 

 ous experiments by vivisection upon animals, especially 

 upon the monkey as possessed of a brain of the same 

 type as that of man, have resulted in greatly extend- 

 ing our knowledge respecting this localization of func- 

 tions in the cortex. We cannot follow the method and 

 progress of discovery, but some of the conclusions have 

 been referred to in preceding chapters and others may 

 be mentioned here. 



In respect to some of the highest mental operations 

 the brain probably acts as a whole through the immense 

 number of associational fibers connecting all parts of the 

 cortex, so that no physiologist is able to say that thought 

 is located in certain cells of that convolution, or memory 

 or imagination in another. But it is still correct to say 

 that certain groups of cortical cells are concerned in a 

 peculiar way with certain sensations or with certain 

 movements. 



454. Motor Areas. It has been found that when the 

 surface of an animal's brain is laid bare and an electric 

 surrent is applied to the convolutions, the stimulation of 



