CHAPTER XIX 



THE STRUCTURE OF THE CEREBRAL CORTEX 



THE preceding pages have included a brief chapter on some of 

 the general biological principles underlying the differentiation of 

 the structure and functions of the nervous system, some general 

 characteristics of the nervous tissues, a brief survey of the 

 structure of the various great divisions of the nervous system, 

 and finally an analysis of the more important sensori-motor 

 reflex circuits. Nearly all of the mechanisms hitherto consid- 

 ered are concerned with the innate invariable types of response 

 represented in the reflex and instinctive life of the organism 

 (p. 31). In the higher mammals, and especially in man, the 

 individually acquired relatively variable types of action, par- 

 ticularly those which are consciously performed, require the 

 cooperation of the cerebral cortex, and the following chapters 

 will be devoted to a consideration of the cortex, its structure, 

 functions, evolution, and biological significance. 



We have already commented (pp. 109, 215) on the fact that the 

 cerebral cortex appeared later in vertebrate evolution than most 

 of the other parts of the brain, and that in general it serves the 

 individually acquired and intelligent functions, in contrast with 

 the brain stem and cerebellum, which contain the apparatus for 

 the innate activities of the reflex type. The primary reflex 

 centers of the brain stem and cerebellum, accordingly, are some- 

 times called the old brain (palaeencephalon, see Fig. 45, p. 114), 

 while the cerebral cortex and those parts of the brain stem which 

 develop as subsidiary to the cortex (such as the neothalamus, p. 

 163) are called the new brain (neencephalon). 1 



1 A review of the evolution of the brain and the phylogenetic origin of 

 the cerebral cortex would lie beyond the limits of this work, for the liter- 

 ature upon this subject is very extensive. The following papers may be 

 consulted in the present context. (See also the bibliographies on pp. 

 159, 223.) 



HERRICK, C. JUDSON. 1910. The Evolution of Intelligence and Its 

 Organs, Science, N. S., vol. xxxi, pp. 7-18. 



SMITH, G. ELLIOT. 1910. The Arris and Gale Lectures on Some Prob- 



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