268 Tin' Cerebral Cortex in Fells Domestieus 



Fibre Arrangement, 



It is a part in which the fibre supply is poor, and in which there are no large or even 

 medium-sized constituents. 



Cell Lamination. 



The cell endowment is likewise on a poor scale. Following an ordinary plexiform layer, come 

 small pyramidal or polymorphous cells, then a deep lamina of pyramids not exceeding medium size, 

 and, finally, a layer of spindle-shaped cells. 



This may be taken as the general type : two variations occur. 



Variation A. 



The part immediately investing the genu and anterior half of the corpus callosum shows a 

 layer of small, but very sharply stained (chromophilous) lanceolate cells, placed on a level corre- 

 sponding with the inner lamina of large pyramidal cells of other parts. These are reminiscent of 

 similar cells seen in the pregenual area of the human brain ; their presence occasions no appreciable 

 alteration in the fibre arrangement. 



Variation B. 



The second variation occurs behind the splenium. Here, while the fibres remain small, thnv 

 is a distinct increase in their number, and an especial accumulation at the level of the line of 

 Baillarger. 



The cell lamination gives signs of compression by the mid-brain, and is curious. After a 

 deep plexiform layer comes a lamina, eight to ten cells deep, composed of closely packed, small, 

 oval elements, with the long axis placed parallel to the surface. Then follows a layer, in which 

 stunted and indifferently stained pyramidal cells of medium size are mixed with cells, smaller but 

 more deeply stained, and lastly, the fusiform cells are flattened so that their long axis is horizontal 

 instead of vertical. 



PREFRONTAL AREA. 



This area includes cortex on the mesial surface, in front of the limbic area, and, on the lateral 

 surface, in front of the orbital fissure. 



In sections stained for nerve fibres, the general supply is poor, but there are many medium- 

 sized elements which were absent in the limbic area. 



The cell lamination is uninteresting. The most prominent elements pertain to the internal layer 

 of large pyramidal cells, but although greater in size than corresponding cells in the limbic area, 

 they are hardly deserving of the name large. 



LOBUS PYKIFORMIS. 



Roughly speaking, the lobus pyriformis is divisible into two fields, an outer and an inner, 

 indicated as Olfactory A and Olfactory B in the figures. 



The outer field, Olfactory A, is the more interesting of the two, and its structure corresponds 

 with that found in the pyriform lobe of man. 



In sections stained for nerve cells one observes a deep plexiform layer, and then a prominent 

 band of large well-stained, polymorphous cells (fusiform, triangular, stellate, etc.) with sharp processes 

 pointing in all directions. The lamina is not broken up into nests, as it is in primates, but, in the 

 posterior part, shows signs of being irregularly interrupted. 



