x] Frontal and /'rcfroiifaf, Areas 235 



having a few distinct chromophilic particles; and it may be stated in general terms that 

 proceeding from here forwards there occurs a steplike numerical and volumetrical diminution 

 of these elements. Thus, in the region labelled "frontal," although the lamina is still readily 

 defined, and although the constituents compared with those above-mentioned look similar in 

 shape ami under a good lens a few chromophilic particles can be identified, still when a series 

 of cells is taken and outlined with the camera lucida, the relative difference in size becomes 

 patent; 7iioreover the cells of outstanding size become as uncommon as the large medullated 

 fibre has been seen to be. There are other differences of a minor character, for instance the 

 layer becomes contaminated with other cells of a like shape but much smaller diameter, 

 and also, on account of the closer approximation in size the upper elements are difficult to 

 distinguish from those pertaining to the layer of medium-sized pyramidal cells. 



Advancing next to the " prefrontal " area it is noticed that the cells lose their plump 

 figure and assume an elongated pyramidal form, that even under the highest powers of the 

 microscope chromophilic elements are difficult to detect in them, and that the diminution in 

 size as well as in number is pronounced ; associated with this the layer exhibits a manifest 

 reduction in depth, and indeed, the "prefrontal" cortex can be pointed to as that in which 

 the general representation and the process of specialisation in the external layer of pyramidal 

 cells are far behind that seen in any other part of the brain surface. And on coupling these 

 appearances with what has been said regarding fibre arrangement it will be realised how 

 well the law expressed elsewhere is borne out, that small cells and small fibres always run 

 in association. 



The Layer of Stellate Cells. 



The point of interest about this layer is that it gains in breadth and definition as we 

 proceed forwards ; thus, from being almost unrecognisable in the " intermediate precentral " area 

 it becomes a distinct lamina in the " frontal " and " prefrontal " fields ; at the same time it 

 cannot be said to equal what we have seen, for instance, in the temporal and parietal regions, 

 it may have the same breadth, but its constituents are not nearly so closely aggregated, nor 

 is the columnar arrangement so obvious. 



Internal Layer of Large Pyramidal Cells. 



The representation of this layer suffers in much the same way as the corresponding 

 external layer. In the " frontal " region the component cells are very obviously less numerous 

 and also smaller than they are in the "intermediate precentral" area, while in the "prefrontal" 

 field the deterioration is profound, so much so that the largest cells seen are only equal in 

 size to the elements in the layer of medium-sized pyramidal cells of other regions, and 

 altogether they form a very indefinite layer. 



Layer of Fusiform Cells. 



A fusiform layer is plainly discernible throughout the frontal lobe but in the " prefrontal " 

 region the contained cells are all exceedingly small and delicate. 



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