78 In ft' r mediate Postcentral Cortex [CHAP. 



It has been noted already, that although cortex having typical postcentral characters 

 can be followed along the posterior wall of the fissure of Rolando down to its lower extremity, 

 it usually recedes from the surface a centimetre or more above this point, so leaving the 

 whole of the superficial part of the lower end of the ascending parietal gyrus covered by 

 intermediate cortex. And, such cortex extends a short distance below the extremity of the 

 fissure of Rolando, but apparently not on to the operculum, although in this situation, on 

 account of the fusion of the intermediate pre- and post-central types, the definition of the 

 boundary is difficult. 



Distribution of the Intermediate Postcentral type in the Anthropoid Ape. (Plate II.) 



In the brain of the first chimpanzee examined, in which the calloso-marginal fissure 

 followed a course like that in the human brain, this area also had a human distribution, 

 but in the case of the second chimpanzee and also in the orang, an irregular arrangement 

 of the tail of the calloso-marginal fissure made it difficult to locate the posterior limit of 

 the field on the mesial surface, and also along the upper margin of the hemisphere. 



FUNCTIONS OF THE POSTCENTRAL AREAS. 



While from the functional point of view our knowledge of the postcentral region is 

 wrapt in obscurity, the road to its further consideration and investigation has been cleared, 

 although in a negative manner, by the experimental researches of Professors Sherrington and 

 Griinbaum, referred to in the preceding chapter; because these researches clearly show that 

 the postcentral gyrus, whatever else its function may be, must be ousted from the position 

 it has held for so many years as part of the motor area. 



Briefly recapitulating the evidence on this point, we find that in the long series of 

 experiments conducted on anthropoid apes by the above-mentioned observers, never, save under 

 exceptional circumstances 1 , were responsive movements obtained from electrical excitation of 

 the postcentral gyrus; again, not only was this convolution "silent" when exposed to the 

 influence of electrical stimulation, but ablation measures proved as negative in the production 

 of motor paralysis as similar measures had proved positive in the case of the precentral 

 gvrus. Moreover, on extending their experiments to lower members of the ape family the 

 animals, be it noted, which afforded material for earlier workers in this province there 

 was a repetition of the negative results, thus annulling the possible contention which might 

 be exploited by previous experimenters that the anthropoid differs from the lower ape in 

 regard to the distribution of its motor area. It is unnecessary for me to pursue this question 



1 On account of the cost and difficulty attending the obtainrnent of anthropoid apes Professors Sherrington and 

 Griinbaum spared no effort to make full use of the animals which came into their possession, accordingly after 

 they had served their immediate purpose as means to the determination of the motor area they were always further 

 employed as material for other scientific investigations. Now one animal, in which the influence of the typhoid 

 bacillus was being studied, developed typical meningitis over the cortical area previously laid bare, and I am informed 

 that a repetition of the stimulation measures on the cortex so inflamed produced responsive movements not only from 

 the precentral but also from the postcentral gyrus. But this result, which must be looked upon as an extraordinary 

 one, is fully commented upon in Professors Sherrington and Griinbaum's paper. 



In other cases the interesting fact was disclosed that movements ordinarily obtained by excitation of the 

 preceutral gyrus were elicited more readily when the postcentral gyrus was coincidently stimulated at the same 

 horizontal level. 



