76 



Intermediate Postcentral Cortex 



[CHAP. 



STRUCTURE OF THE INTERMEDIATE POSTCENTRAL AREA. 



A. TYPE OF ARRANGEMENT OF FIBRES. 

 (Plate I and Plate V, fig. 2.) 



As is the case in the " precentral " area, so also in the " postcentral " region, the 

 transition from the "typical" to the "intermediate" type of arrangement takes place gradually; 

 however, if in a transverse section of the postcentral gyms the arrangement of fibres in 

 the cortex be carefully traced round from the Rolandic to the parietal side, the following 

 changes will be found to occur. (1) The zonal layer, which is poorly developed to begin 

 with, becomes fainter still, and those large medullated fibres, which were described as being 



FIG. 7. Eadiary zone in intermediate postcentral area x Afi. 



Under a high power the fibres of large size seen in the postcentral area proper (Figure 5) 

 have to a great extent vanished. 



occasionally present at this level on the Rolandic side of the gyrus, vanish altogether; (2) in 

 like manner, the supraradiary plexus loses in wealth of fibre representation. (3) The line of 

 Baillarger, while retaining its width and position, becomes obviously less dense, and owing to 

 the relative paucity of fibres of medium calibre its depth of staining is not so intense. (4) Since 

 the radiations of Meynert cease to contain coarse medullated fibres, the fasciculi lose their bold 



