vm] Parietal Arc 201 



;i bundle. None of the fibres seem to project higher than the inner part of the supra- 

 radiary field. 



Radiary Zone. 



In describing the radiary zone it is best to compare it with that of surrounding areas. 

 Now in the adjoining gyrus fornicatus and in the " common temporal " area we noticed 

 that this zone was palely stained, and especially that it was lacking in long fibres of 

 medium size and entirely wanting in fibres which could be called large. In this area, 

 on the contrary, fibres of medium size are present in considerable abundance ; moreover, 

 large fibres are occasionally seen. But the latter are less numerous than they are in the 

 " intermediate postcentral " area and infinitely less abundant than in the contiguous " visuo- 

 psychic " cortex. 



The fibres of the interradiary plexus are difficult to dissociate from those which may 

 more properly be regarded as pertaining to the inner line of Baillarger. 



Easily defined on the limbic and occipital sides, the postcentral and temporal boundaries 

 are not so readily determined ; however, placed in order of sequence as regards fibre wealth 

 in the radiary zone, it may safely be said that the " intermediate postcentral " cortex comes 

 first, then the "parietal," and the "common temporal" last. It is chiefly by judgment on 

 this general fibre representation in the radiary zone that the area can be differentiated. 



TYPE OF CELL LAMINATION. (Plate XX, fig. 2.) 

 Plexiform Layer. 



Not differing markedly from that of surrounding fields this layer calls for no special 

 comment. 



Layer of Small Pyramidal Cells. 



So far as can be judged from Nissl preparations this layer also exhibits no feature 

 which can be considered characteristic. 



Layer of Medium-Sized Pyramidal Cells. 



The constituents of this lamina resemble those seen in the postcentral areas and are 

 present in about the same number. 



External Layer of Large Pyramidal Cells. 



As the determination of the topography of the " parietal " field is assisted by comparing 

 these cells with corresponding cells in adjacent areas, it is important that they should be 

 fully considered. 



The size and number of the contained elements and its general depth are sufficiently 

 great to confer easy definition on the lamina. 



Comparing it first with the corresponding layer in the " intermediate postcentral " area, 

 it must be admitted that the difference is not a great one ; nevertheless, on careful 

 inspection, and especially on making a series of camera lucida drawings of cells under a high 



C. 26 



