228 D. DAVIDSON BLACK 



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Owing to the great modification of cell lamination brought 

 about by the presence of thalamic projection fibers in the plexi- 

 form layer of the cortex in certain regions, it is not considered 

 advisable to attempt to compare in detail the type of lamination 

 found in such regions with that normally occurring in the devel- 

 oping cortex. In areas remote from such disturbing influences, 

 however, such comparison may, I think, be safely made. 



In figure 16 it was noted that layer III apparently corresponded 

 to Bolton's inner fiber lamina (2). The inner fiber lamina in 

 the normal developing cortex is a layer which develops as the 

 result of a separation of the cortical neuroblasts into an outer 

 and an inner cell lamina. The polymorphic layer of the normal 

 adult cortex is derived from the inner cell lamina, while practi- 

 cally the whole cortex above the inner line of Baillarger is derived 

 from the laminae superficial to this. If, then, layer III repre- 

 sents the inner fiber lamina, it would appear that the outer 

 layers of the cortex in this case are in a state of sub-evolution. 

 For the total thickness of layers I to III inclusive is less than 

 that of the much thickened polymorphic layer (IV and V). The 

 somewhat closely packed lamina of cells constituting layer IV, 

 which is well developed over most areas of this cortex, appears 

 to be peculiar to this case and not comparable to any layer nor- 

 mally present at term. In the case reported by Naegeh (17) 

 however, a layer of apparently similar nature is shown in his 

 figure 42. It would thus seem that the cortex had begun its 

 development from within outwards in this region, as is normally 

 the case. 



At first sight it appears difficult to account for the greatly 

 increased thickness of the cortex in a cerebrum in which cell 

 differentiation has been described as subnormal. This difficulty 

 is only an apparent one for, as will be subsequently pointed out, 

 there is evidence in this brain to show that at least the greater 

 part of the undifferentiated normal pallial anlagen are present. 

 The surface area of the cortex, however, has not been increased 

 by the formation of cerebral convolutions. Thus a large num- 

 ber of cell elements have to accommodate themselves over a lim- 

 ited area, resulting in the increased thickness of the cortex which 



