CHAPTER VII 



THE ORIGIN AND SIGNIFICANCE OF 

 CEREBRAL CORTEX 



THE PROBLEM 



THE human brain is the most complicated piece of mechanism 

 that we know, and the products deHvered by this thinking 

 machine are, for us, the most interesting. Detailed descriptions of it 

 and some of its operations have been written, but where and how it 

 fabricates its unique wares is still the basic problem of science and 

 philosophy. Thinking is a part of our living, and apparently we think 

 all over, just as we live in all parts of our bodies. Yet it is evident 

 that some parts of us play crucial roles in our mental life, just as other 

 parts do in our movements, our digestion, and so on. That the 

 cerebral cortex as a whole is a specific organ of much of our mental 

 life is as well established empirically as anything in biology, but how 

 thinking is done and where the critical processes are carried on are 

 still mysterious. 



Study of origins and early stages of embryologic and phyletic de- 

 velopment has resolved many biological and psychological problems, 

 but essential features of the inception of cerebral cortex remain ob- 

 scure. Interest in this theme instigated my program of research upon 

 the amphibian nervous system. All reptiles possess well-organized 

 cortex, that is, superficial laminae of gray substance in the pallial 

 part of the cerebral hemisphere, simple in pattern but obviously com- 

 parable with, and ancestral to, the human cortical complex. They 

 also exhibit enormous enlargement of some subcortical parts of the 

 hemisphere, notably the strio-amygdaloid complex. In birds these 

 subcortical areas are still further enlarged and complicated, with 

 reduction in the amount and specialization of the cortical tissue. In 

 mammals the subcortical parts of the hemisphere are relatively 

 smaller, some of their functions apparently having been taken over 

 by the progressively expanding cortex ('21, p. 452; '26, p. 122). 

 Correlation of these structural peculiarities with the characteristic 

 modes of life of these several classes of animals gives some clues to 

 the significance of the cortex in the vital economy. 



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