iv] Postcentral or Senxorn Ar< 71 



l Variations in tln> Punt cent ml Type of Fibre Arrangement, 



We found that topical variations occurred in the " precentral " area; it is the same in 



the " ])ust central " field. 



To begin with, a section from the upper end of the area is easily distinguishable from 

 one from the lower extremity, and this is so principally because, proceeding from above 

 downwards, there occurs a gradual and progressive diminution in the number, and also in 

 the calibre, of those large fibres which have been described under the headings of inter- 

 radiary plexus and association fibres. It so comes about, that a section from the lower end of 

 the " post-central " area bears a resemblance to one from the upper end of the " intermediate 

 postcentral," tor the same change takes place in the latter field. 



According to Passow, the general fibre wealth of the cortex of the postcentral convolution 

 begins by increasing from above downwards, it reaches a culminating point about two-thirds of 

 the way down, and then gradually diminishes again. But this certainly does not apply to tin- 

 large fibres to which I have referred, for I can state, without hesitation, that they exhibit 

 their best development in the small portion of the " postcentral " area on the mesial surface, 

 and along the upper third of the area on the lateral surface of the hemisphere, and the 

 diminution in wealth is, as I have said, progressive from the beginning. 



In its bearing on other layers and systems of fibres I am also inclined to doubt the 

 correctness of Passow 's statement ; in the zonal layer for instance, it is in the upper 

 part of the area, and here alone, that large medullated fibres are recognisable; again, the 

 richness of the plexus in the supraradiary layer diminishes without intermission from above 

 downwards ; and, finally, there is no question that the line of Baillarger is denser in the 

 upper part of the area than in the lower, although its breadth remains stationary in all parts. 



In connection with this line, I may mention incidentally, that in the brain of the female,- 

 aet. 37, it formed a much more prominent band than it did in the brain of the male, aet. 29, 

 or of the female, aet. 21, and as the sections in all cases were stained in precisely the same 

 manner, confirmation is given to Kaes' statement that its development proceeds progressively 

 up to the age of maturity. 



B. TVPE OF CELL LAMINATION IN THE POSTCENTRAL AREA. (Plate III, fig. 2.) 



Plexiform Layer. 



The plexiform layer looks shallow when compared with that of the " precentral " cortex, 

 but Nissl specimens reveal no noteworthy differences of constitution. 



Layer of Small Pyramidal Cells. 



This layer seems to possess a slight advantage over the " precentral " layer in point of 

 depth, likewise the cells are more numerous and give the lamina a crowded appearance, 

 but in regard to cell size and shape there is no noteworthy difference. 



