CHAPTER IV. 

 POSTCENTRAL AND INTERMEDIATE POSTCENTRAL AREAS. 



iNTBonrcToKY REMARKS. 



IT seems that behind the fissure of Rolando types of cortex exist, having a distribution 

 which forms a counterpart to that observed in the pre-Rolandic area, for just as the posterior 

 or Rolandic half of the precentral or ascending frontal convolution is found to be coated 

 by a special type of cortex, and invested in the frontal direction by another type inter- 

 mediate in character, so also the anterior or Rolandic half of the postcentral or ascending 

 parietal gvrus is covered by a special type, which in turn is invested in the parietal 

 direction by an intermediate arrangement. But with distribution the analogy ceases, for, as I 

 shall show in the immediately following pages, the structure of the postcentral cortex, not only 

 in the human being, but also in the anthropoid ape, differs in many essential points from 

 that of the precentral : indeed, the histological disagreement is so pronounced as to suggest 

 in itself a difference in function. 



Reflecting on the nlle probably played by this area, it seemed that profit might be 

 gained by directing further investigations towards proving whether or not it represented the 

 cortical terminus for common sensation; accordingly, it became part of my programme to 

 procure suitable material and make an exhaustive microscopic examination of the ascending 

 parietal gyrus in diseased conditions, involving a severance of the chain of sensory neurones" 

 at various levels: thus, instances of severance of the tract in its intracerebral course were 

 supplied bv cases of old-standing capsular lesion, instances of interruption at the level of the 

 spinal cord by cases of Tubes dorsal in, and instances of peripheral section by cases of amputation. 

 This branch of the research has furnished results having a most important bearing on the 

 question of sensory localisation, those dealing with Tabes dorsalis being of special interest. 



Then, since much of the evidence I have to bring forward is out of harmony with current 

 doctrines, it has been deemed necessary to give due consideration to the conflict of views on the 

 function of the postcentral region, and on the question of the cortical localisation of common 

 sensation in particular, and to this the concluding section of my chapter is allotted. 



STRUCTURE OF THE POSTCENTRAL AREA. 



To the two vertical parallel-lying areas (vide Plate I) into which the postcentral or ascend- 

 ing parietal cortex is divisible, the names " postcentral " and " intermediate postcentral " are 

 respectively applicable. It will be convenient to consider these two areas separately, and we 

 will take the "postcentral" field first, and open with a description of the arrangement of fibres, 

 incidentally pointing out the manner in which the arrangement differs from that of the "pre- 

 central " area. 



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