iv~) P(nft(Tiifi'<d or Sciixorn Arm 75 



Layer of Fusiform Cells. 



This layer does not call for special comment, as the elements it contains resemble 



those met with in most other parts of the cortex. 



Distribution of t/ie Postcentral Area. (Plate I.) 



Roughly speaking, the postcentral type of cortex is distributed over the anterior half 

 of the posteentral convolution on the convex surface of the hemisphere, and like the precentral 

 formation it crosses the upper margin of the hemisphere on to the mesial surface, to cover 

 a small tongue-like area situated on the paracentral lobule, immediately behind the upper 

 extremity of the fissure of Rolando. Anteriorly (on the mesial aspect) it lies in contact with 

 the upper extremity of the " precentral " area ; and, below and behind, it is enclosed by 

 the " intermediate postcentral " area, which in turn is limited by the calloso-marginal fissure. 



In those brains in which the fissure of Rolando does not cross the upper margin a 

 postcentral strip of cortex is still found on the mesial surface, and its anterior boundary is 

 then formed by a line drawn downwards, continuous with that fissure, and parallel with the 

 calloso-marginal tailpiece. We thus see, that on the mesial surface the position and extent 

 of the area is directly influenced by the upper extremity of the fissure of Rolando. 



At the upper margin of the hemisphere the area is slightly narrower than it is elsewhere. 



On the lateral surface, the fissure of Rolando again forms a most important and definite 

 boundary, for the whole of the anterior wall of the postcentral gyrus, down to the very floor 

 of that fissure, is covered by " postcentral " cortex. On the free surface of the gyrus the 

 change in character from " postcentral " to " intermediate postcentral " cortex does not take- 

 place abruptly, still it is approximately correct to describe the dividing line as running down 

 the centre of the gyrus. Inf'eriorly, however, while cortex having " postcentral " characters can 

 be followed on the posterior wall of the fissure of Rolando down to its extremity, it generally 

 recedes from the surface about a centimetre above this point, so leaving the exposed part 

 of the lower end of the ascending parietal gyrus covered by " intermediate postcentral " cortex. 



From the above account it is quite obvious that as the major portion of the " post- 

 central " cortex lies concealed within the fissure of Rolando, it is impossible to give a correct 

 representation of its distribution in a surface diagram. 



The Postcentral Cortex in the Anthropoid Ape. (Plate II.) 



As regards character, a type of cortex can be made out in the brain of the man-like 

 ape which bears an extraordinary resemblance to that obtaining in the human being; in 

 fact, the appearances may be briefly described as being a reproduction in miniature of the 

 human features. 



The same similarity holds in regard to distribution, and in all three brains examined 

 the area has stood in the closest relation to the fissure of Rolando. 



102 



