266 Tlie Cerebral Cortex in Felis Dotnesticus 



pallor of course denotes a diminution in fibre wealth, and the loss affects all layers and systems of 

 fibres but, and this is of some importance, the radiations of Meynert, although attenuated, still 

 contain a few fibres of fair size, and in the depths, partly in the interradiary plexus and partly 

 in the white substance, fibres of large calibre, many of which seem to be cut transversely, are still 

 present. 



The presence of such large fibres serves to distinguish this cortex from the subjacent limbic 

 cortex. 



Cell Lamination. 



The layer of small pyramidal cells is followed by one of medium-sized elements which increase 

 in magnitude as the layer is descended, but do not attain the size of large pyramidal cells ; 

 indeed, it is a noteworthy feature of this cortex that there is no external layer of lai-ge cells. 

 A stellate layer, also, is very difficult to define. But there is an important lamina of large internal 

 pyramidal elements ; not so large as the average representative of the same layer in the sensory 

 or postcruci;il cortex, these cells are curious in being very much elongated and in staining very 

 intensely and uniformly. 



A layer of fusiform cells is present but devoid of special interest. 



Distribution. 



The area occupies all that part of the gyrus marginalis intervening between the sensory and 

 visual areas ; it also oversteps the lateral fissure, and, as the diagrams show, runs backwards along 

 the mesial half of the suprasylvian gyrus. 



It must finally be mentioned that this cortex presents most typical characters in its anterior 

 half, and that, on the confines of the visual area, the arrangement of the fibres especially under- 

 goes some change it loses in richness so that I may be wrong in calling this all one area. (The 

 field marked with dots in the diagrams is here referred to.) 



ECTOSYLVIAN REGION. 



The ectosylvian region embraces all those gyri investing the Sylvian fissure and lying within the 

 confines of the suprasylvian sulcus. 



The cortex of this part differs from that on the convexity in having no cells of large size, 

 and also an inferior supply of nerve fibres ; these are general characters. On closer examination 

 it is divisible into two sub-areas, indicated by vertical streaks and cross-hatching in the figures. 



We will take the lower of these areas first. 



ECTOSYLVIAN AREA A. 

 Fibre Arrangement. 



I have given independence to this area chiefly on account of some peculiarities in the fibre 

 arrangement. On examining fibre sections one observes nothing distinctive in the outer layers, but 

 in the depths, streaming up from the white substance and for the greater part obliquely placed, 

 are numbers of fibres of medium size giving rise to quite a dense plexus. It seems clear that these 

 pertain to some fasciculus emerging from the white substance to impinge hereabouts, and that they 

 are destined for cells confined to this part is likely, because the cell lamination exhibits corre- 

 sponding peculiarities. 



Cell Lamination. 



There is an ordinary plexiform layer. 



A small pyramidal layer is present, but the components are scanty, so also are the medium-sized 

 pyramidal cells, although their shape is perfect. 



