1932] PoUak: Afferent Fiber Sysfetm, Primate Cerebral Cortex 229 



in the calcarine fissure. On the other hand it is obvious that areas 18 

 and 19 as well as areas 20 and 21 and the g:reater portion of area 22 of 

 Brodmann in the brain of the monkey lie outside the projection fields 

 of the hemisphere and offer us, therefore, the opportunity to study 

 their functions by partial or by complete ablation/ 



New prospects are also opened for the further investigation of the 

 special functions of distinct cytoarchitectural areas in conscious sub- 

 jects as practiced by Gushing, Krause, Valkenburg:, Foerster, Man- 

 kowski, and others, as well as for clinical, pathological, and anatomical 

 studies. With respect to the somatic sensory cortex, for example, it 

 will be necessarj^ to bear in mind that the "nuclear or focal zone" of 

 that cortex is completely sunk in the sulcus centralis and does not 

 reach the convexities either of the anterior or of the posterior central 

 convolution. 



In conclusion a few words may be permitted concerning general 

 ways and means of experimental brain research. If experimental 

 anatomical, physiological, and psychological research is to shed more 

 light on the mechanisms and the nature of the highest nervous pro- 

 cesses in man, this can scarcely be achieved by using lower mammals. 

 In these it is difScult to produce sufficiently localized injuries, con- 

 fined to definite small portions of the cortex, to certain cytoarchitec- 

 tural areas or regions, without damaging other areas and the sub- 

 cortical white mass, or even disturbing the entire brain, not to men- 

 tion the danger arising from the application of the results obtained 

 with primitive brains to human conditions. The brain of the lower 

 primates is, on the contrary, in its essential features and in its finer 

 structure a simplified replica of the human brain. This fact, together 

 with the comparatively large size of the monkey's brain, makes 

 orientation and the technical aspect of the work more certain and 



1 No less important is a systematic study by areas of the association, callosal, 

 and efferent fiber systems of the cerebral cortex, preferably vnth the help of 

 Marchi's method. The next task will be a systematic study of finer structures 

 of the cortex with the help of Golgi's and Ramon y Cajal's silver impregnations. 

 Finally, much could be expected from a study of special areas (the striate area in 

 the monkey, for example) with regard to the preservation of "figures" in subcor- 

 tical centers (the external geniculate body). After producing small, strictly cortical 

 lesions representing various figures, the resulting degenerated portions of the 

 subcortical nuclei should be determined with the help of the Nissl's method 

 (Nissl's "primary irritation"), mapping their extent, shape, and position. The 

 same could also be done with the somato-sensory and auditory cortex by examining 

 the degenerated figures in the thalamus and in the internal geniculate body in a 

 way similar to that applied in our Experiment V-c. (A similar metliod, though 

 only for a less exact purpose, was applied by Heuven in his recent study of the 

 visual system.) 



