THE EVOLUTION OF THE BRAIN II3 



appropriated by evolutionary steps all that body of nervous 

 activity that we associate with conscious Hfe and voHtional 

 effort. What the hemispheres have thus taken over is by 

 no means all of our nervous doings. The lower part of the 

 brain stem, the spinal cord, and such subsidiary centers as 

 the sympathetic system have buried within them an untold 

 mine of nervous activity that never really reaches this upper 

 level but that nevertheless has potentialities which are only 

 beginning to be appreciated in the study of the subconscious. 

 That which has emerged in the course of the differentiation 

 of the hemispheres in the higher vertebrates occupies a 

 place quite separate from that of the original olfactory 

 centers and represents in a measure a novel system super- 

 imposed upon the older olfactory brain. This new growth 

 within the hemispheres, chiefly visible in the mammals, 

 is astoundingly expanded in man in whose brain it is repre- 

 sented by the relatively enormous convoluted surface so 

 characteristic of the exterior of that organ. This growth is 

 called the neopallium and in the higher animals it has so over- 

 grown and overshadowed the ancient brain stem as to have 

 reduced this primitive part to relative inconspicuousness. 



In the neopallium of man take place all those complicated 

 activities that we associate with personality. Here resides 

 our mental life — our sensations, memories, and volitions; 

 here imagination has its play, and here too when maladjust- 

 ments occur moods arise and insanity may reign. Descartes 

 believed that the pineal body was the seat of man's soul, 

 but modern science knows that the neopallium is the correct 

 location. Here all that is most characteristic of us takes 

 place and in fact the activity of the region is in all prob- 

 ability a manifestation of our real inmost selves. 



Thus the evolution of the brain of man finds its roots in 

 those elemental nervous operations connected with the 

 muscular responses of such simple animals as the sea anem- 

 ones whence have sprung the differentiated sense organs and 

 central nervous organs of higher animals. By the conversion 

 of these sense organs from surface receptors to distance 

 receptors and by the simultaneous growth of central organs 

 as repositories of experience there has been established in the 

 hemispheres of the mammals and particularly of man that 



