iv] Poxti-t'ittral or Sensory Area 99 



and sensory troubles, while the reports of the results of limited lesions are not free from the 

 objection that the microscope might have revealed injury to the fibres pertaining to both gyri, 

 and this all apart from the acknowledged difficulties besetting the experimenter in detecting 

 and forming accurate judgments upon delicate sensory disturbances in dumb creatures. 



Among histologists, Flechsig makes a bolder stand than any in favour of the double function 

 of the central gyri, but at the present time his statement that the fibres of his sensory 

 system marked No. 1, and these are the first to develop, are chiefly distributed in the cortex 

 of the posterior central gyrus might be taken up by his opponents as one of the strongest 

 arguments against that view : however, as I have said before, we await further details con- 

 cerning the course of the developing "cortical lemniscus" from Professor and Madame Vogt, 

 and it will be wiser not to lay stress on Flechsig's finding until these are forthcoming. 



Turning next to a consideration of the arguments which have been used in support of 

 the contrary view that the motor and sensory areas are not coincident, we find that this cause 

 is espoused in no hesitating manner by von Monakow. This writer maintains that to produce 

 hemianaesthesia, and likewise degeneration of the lemniscus, an extension of the lesion from 

 the " motor zone " into the parietal lobe is a sine qua non, and this view, originally developed 

 from experimental studies, he believes to be confirmed bv observations on the human subject. 

 When von Monakow wrote it was taken for granted that the postcentral gyrus was motor, 

 and I am curious to know whether he has now modified his views. To me it seems that 

 the conclusions he has drawn are on the whole sounder and more approximately correct than 

 any which have hitherto been offered, but I prefer to reason that the crossed anaesthesia, 

 in the condition referred to, is purely attributable to the destruction of the postcentral 

 gyrus, although I look upon his statement emphasising the necessity of an extension of the 

 lesion into the parietal lobe as one full of significance. And, concerning his inference that a 

 specific sensory centre exists in the parietal lobe proper, my histological researches, as I shall 

 show in the next chapter, lend no colour to such an assumption : I would also say that 

 if sensory disturbances should be noted in consequence of a lesion in this situation, it would 

 be very necessary, in weighing up the case, to eliminate a probable complicating contingency 

 in the shape of an interruption of the sensory fibres which I believe make for the postcentral 

 gyrus. Bnt this is one of the many problems connected with sensory localisation which must 

 be set aside for future solution. 



Of others who argue that sensation has a separate representation in the cortex, Durante, 

 Walton, and Paul look favourably upon the parietal lobe as its residence ; but, as these 

 observers also have not been given the opportunity of adjusting their views in accordance 

 with our present knowledge, nothing is to be gained by discussing what they have written. 



It would likewise be purposeless for me to advance the array of cases published to support 

 the view that the postcentral gyrus is a sensory centre of prime importance, for the objection 

 concerning reconsideration and reexamination lodged against cases advanced for the contrary 

 is equally in force. 



It may be indicated that the observers just quoted, while maintaining that the so-called 

 Rolandic zone has not a mixed sensori-motor function, still argue that the paths for the 

 transmission of sensory impulses impinge on the parietal cortex in close proximity to 

 that zone. 



I have next to mention that there are other eminent neurologists who hold not only 

 that the Rolandic zone has no connection with sensation at all, but that the sensory centre 



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