356 D. DAVIDSON BLACK 



toward typical embryonic arrangement into rows at right angles to the 

 surface of the cortex. 



Layer V. A stratum of less densely packed cells which varies in 

 thickness at the expense of the subjacent lamina. 



Layer VI. An irregular stratum of varying thickness made up of poly- 

 morphic and embryonic elements arranged in groups of various sizes 

 and on the whole showing a denser arrangement of cells than Layer V. 



Area 1 B. Cortex over the inner pillar of the anterior recurved 

 margin of the cerebrum. Average thickness 2.5 or 3 mm. (fig. 5). 



The lamination occurring over this area is essentially similar 

 in its arrangement to that already described for Area 1 A. The 

 cortex is here however markedly thinner and cell differentiation 

 is even less evident. In the zonal layer there are no medium 

 sized multipolar elements to be found. At the cortical limbus 

 all cell laminae blend as described in a previous paper (2) . In the 

 figure the inner or polymorphic layer is interrupted by a shrinkage 

 cleft. 



In both these areas described Layers V and VI are easily to be 

 distinguished as separate strata. Below, Layer VI gradually 

 merges with the medullary center. 



Area 2. Cortex from the anterior part of the right posterior 

 lobe. Average thickness 5.2 mm. (fig. 6). 



Layer I. Well developed but, as may be seen from the figures, it is 

 much thinner than the corresponding layer in the sections described 

 above. In the deeper portion of this stratum or in the upper parts of 

 the subjacent layer there are found not infrequently quite large irregular 

 multipolar elements. When seen they form a marked contrast to the 

 small und fferentiated cells predominating at this level. 



Layer 11. This layer shows no essential difference from Layer II 

 as described in Area 1. 



Layer III. In some places in this region this layer is to be distin- 

 guished only with difficulty. Its presence depends upon the size of the 

 irregular cell groups of the superadjacent layer, which at times almost 

 blends with Layer IV. The cells are small and are mostly of embryonic 

 nature. Occasionally at the junction of Layers II and III there are 

 found medium sized pyramids fairly well differentiated. 



Fig. 6 Section through the cortex bordering the right anterior limb of the Y- 

 shaped median furrow. Area 2, region indicated in figure 3. X 65. 



Fig. 7 Section through the cortex from the central portion of the base of the 

 left posterior lobe. Area 3, region indicated in figure 3. X 65. 



