358 D. DAVIDSON BLACK 



Layers IV and V. These two layers are so blended as to be indis- 

 tinguishable in this region. Together they make up a well marked and 

 densely packed cell stratum which varies in thicloiess considerably at 

 different points. In its deeper portion there occur either singly or in 

 groups, certain giant polymorphic cells averaging 36 by 43 microns in 

 size. 



Layer VI. The polymorphic layer is not sharply marked off from the 

 layer above and the line of demarcation is in places very indistinct. This 

 layer and the superadjacent stratum make up a good two-thirds of the 

 total cortical thickness in this area. 



Area 3. Cortex from the central portion of the base of the left 

 posterior lobe. Average thickness 5 nun. (fig. 7). 



Layer I. The zonal layer is well developed but not very sharply 

 marked off from Layer II. Irregular quite large multipolar elements 

 are of frequent occurrence in this stratum, which is otherwise similar to 

 the corresponding lamina in the areas described. 



Layer II. This layer is not so well developed as is the case in the more 

 anterior portions of the same lobe. The crowding of the cells into irreg- 

 ular islands is not so marked. The most characteristic feature of this 

 layer is the occurrence here and there of giant polymorphic cells averag- 

 ing 33 by 40 microns in size. 



Layer III. This layer is readily distinguished by the sparseness of 

 its cell content but its boundaries are by no means definitely marked. 



Layer IV. This layer is thick and well marked. The majority 

 of the elements in the more superficial portions of the stratum are 

 small and poorly differentiated. The characteristic arrangement into 

 rows or columns is well shown. In the deeper parts of the lamina, 

 numerous well developed medium and large pyramidal elements occur. 

 This part of the stratum is quite evidently in a more advanced state of 

 differentiation. 



Layer V. Though seen in some places, as for instance in the area 

 drawn in figure 7, this layer is to be made out only with difficulty in this 

 region. 



Layer VI. There is a tendency toward grouping of the elements of 

 this layer into irregular islands as was the case in this stratum over the 

 anterior lobe. Otherwise this layer does not differ essentially from 

 the polymorphic stratum of other areas. 



Area 4- Cortex from the posterior pole of the right posterior 

 lobe. Average thickness 5.2 to 6 mm. (fig. 8). 



Layer I. The zonal layer is very thin, being little more than one-third 

 as thick as over other areas of the cortex. 



Layer II. This layer is fairly well marked and is made up of medium 

 and small sized polymorphic and pyramidal elements somewhat loosely 

 arranged. In the outer portion of this stratum large polymorphic cells 



