1932] Poliak: Afferent Fiber Systems, Frimate Cerebral Cortex 67 



intracortical afferent fibers in various areas of the extensive somatic 

 sensory cortex are in perfect accord wath, and would tend to sup- 

 port, the division of the whole central region into several distinct areas 

 more or less parallel with the sulcus centralis. This also agrees with 

 what has been said on the segmentation of the thalamus and of the 

 thalamo-cortical radiation. All this indicates a functional differen- 

 tiation of the whole extensive precentral-postcentral somato-sensory 

 region into several suborgans whose functions cannot be regarded as 

 identical. For the same reason the conception of the precentral cortex 

 as an "accessory" to the "main" postcentral somato-sensory region 

 is also not acceptable, although a close collaboration of all the men- 

 tioned suborgans is more than probable. The question which arises 

 here is : What particular somato-sensory function must be localized 

 in the precentral cortex, and what other forms or qualities of sensi- 

 bility are connected with the postcentral region"? So far, the clinical 

 and the experimental investigations have, beyond a few hints, been 

 unable to give a clear answer to this question, the majority of modern 

 neurologists entirely dismissing the precentral cortex as a possible 

 somato-sensory region. Ransom and Gushing (1909, p. 48 [7] ) in 

 reporting certain sensations of a proprioceptive character when the 

 precentral cortex in a conscious subject was stimulated without move- 

 ments being seen, remain alone ; while Foerster (1927) in his extensive 

 studies, also with conscious subjects, and recently Mankowski (1929) 

 in the same way, evoked both proprioceptive and exteroceptive forms 

 of sensation exclusively when the postcentral-parietal region was 

 stimulated. Minkowski (1917, 1924), in discussing his experiments 

 with monkeys where the precentral region was removed and sensorv^ 

 changes of a proprioceptive character noticed, expressed the opinion 

 that a special form of proprioceptive sensibility, the "unconscious 

 reflex sensibility, ' ' might be localized in the precentral cortex hitherto 

 regarded as purely motor. (See also Bastian and Monakow, 1914, 

 pp. 2'52, 276, 295, 298.) Dusser de Barenne's experiments with mon- 

 keys also point toward a certain somato-sensory function of the 

 "motor" cortex. Foerster (1925, 1927) in connection with the above 

 mentioned experiments supposes that the precentral cortex may play 

 the role of an " accessory somato-sensory region ' ' acting in a vicarious 

 way in case the postcentral "main somato-sensony' region" is damaged. 

 The question of the form or quality of the sensibility to be attributed 

 to the precentral cortex is closely connected with another problem ; 

 namely, whether different forms of sensibility are represented in 

 different cytoarchitectural areas or perhaps in different layers of the 



