1932] Poliak: Afferent Fiber Systems, Primate Cerebral Cortex 9 



differ considerably in the shape, size, and arrangement of their cells 

 and, somewhat less markedly, in their intracortical fibers. But the 

 conclusion which follows from Meynert's formula that only those 

 cortical regions which possess a well developed inner granular layer 

 ("Koniocortex" of Economo-Koskinas) are the receptive fields of the 

 hemisphere must be regarded as an assumption as yet without definite 

 confirmation. (The inner granular layer as a sole criterion of the 

 receptor function of a certain cortical area was rejected by Vogt, 

 1911; compare also Economo-Koskinas, p. 237-9, 542). The somatic 

 sensory function, in some respects in contradistinction to the visual, 

 must be regarded as a complex process. Hence, it is a priori possible 

 that besides the forms of sensation requiring the granular cortex of 

 the postcentral type, other forms of sensation may co-exist which are 

 localized in the ag-ranular cortex of the precentral region. Moreover, 

 the granular cortex extends over the parietal lobe, and it may justly 

 be asked how far the parietal cortex also has its share in the somatic 

 sensory function. (Consider the physiological experiments with 

 conscious subjects performed by Foerster, 1927, and by Mankowski, 

 1929.) Also, as pointed out by Vogt, granules are not entirely absent 

 from the precentral cortex but are only more diffusely distributed 

 therein. (Compare also Economo-Koskinas, pp. 269, 303.) These con- 

 tradictory results of anatomical, physiological, and pathological inves- 

 tigations may suffice to show the vagueness of the arguments on which 

 the present dominant belief in a complete, or nearly complete, separa- 

 tion of the somatic sensory from the motor function in the cerebral 

 cortex is based (at least in so far as the precentral region is con- 

 cerned). Especially does the evidence against any receptor function 

 whatever on the part of the precentral cortex appear inadequate. It 

 would appear that this question can be settled satisfactorily only by 

 establishing upon anatomical evidence whether or not the thalamo- 

 cortical radiation terminates in the precentral cortex, as justly pointed 

 out by Minkowski. (See also the interesting views on the relation 

 between the cortical "sensorium" and "motorium" expressed by 

 Ariens Kappers, 1921, 2, pp. 1201 ff.) 



In the second afferent fiber system of the forebrain cortex, the 

 auditory system, there is scarcely less uncertainty. Here, too, the 

 question whether the "primary" or projectional auditory cortex is a 

 small, well defined area, or whether it extends over a considerable por- 

 tion of the temporal cortex, does not seem to have been settled satis- 

 factorily. The view formerly accepted, that it extends over a large 



