AN ATYPICAL CEREBRAL CORTEX 359 



are of frequent occurrence. The tendency toward arrangement of ele- 

 ments into island-like groups is not so marked as is the case in this 

 stratum over other areas. 



Layer III. Though not well developed, this layer can for the most 

 part be distinctly made out and presents no special peculiarities. 



Layer IV. This lamina is markedly developed and is somewhat thicker 

 than all the strata superficial to it combined. It is made up of a dense 

 collection of cells of embryonic, pyramidal and polymorphic types. 

 The crowding of the elements here is not so great, however, as is the case 

 in this stratum over the anterior lobe and there is a relative predominance 

 of quite well differentiated cells. 



No lamina corresponding to Layer V in the areas already described 

 can be made out in this region. 



Layer VI. The line of demarcation between this and the superad- 

 jacent stratum is very indistinct. The polymorphic layer is here very 

 thick, being thicker in comparison to the total depth of the cortex here 

 than is the case in any other region except in Area 5. Large polymorphic 

 cells — 21 by 36 microns on the average — occur singly and in groups at 

 different levels throughout this stratum. 



Area 5. Cortex from the region of junction of thalamus and 

 cerebrum. Average thickness 6.6. to 7 mm. (fig. 9). 



Layer I. The zonal layer is well marked and shows a peculiar coarse 

 reticulated appearance clue to the presence here of great numbers of 

 large thalamic projection fibers. At the periphery of this stratum there 

 is a layer of small embryonic or neuroglial elements. 



Layer II. The line of demarcation between this layer and the pre- 

 ceding is very indefinite. Numerous large and medium sized polymor- 

 phic elements, together with small embryonal cells malce up this stratum 

 The embryonic elements, however, by no means predominate there as is 

 the case in this stratum elsewhere in the cortex. 



No lamina corresponding to Layer III in other regions can be distin- 

 guished here. 



Layer IV. This stratum is indistinctly marked off from the layers 

 above and below it. It is a thick lamina whose elements show a decided 

 tendency to become progressively smaller in size from without inward. 



There is no lamina corresponding to Layer V as described over the 

 anterior lobe. 



Layer VI. This is a very thick stratum and is poorly marked off 

 from Layer IV. The elements are occasionally arranged in groups of 

 irregular size in which the cells are more closely packed than in the inter- 

 vening spaces. At various levels in this stratum, but more especially in 

 the middle third, there are found certain very large giant cells occurring 

 either singly or in groups of two or three. Many of these cells are as 

 large as 36 by 54 microns but the average size is about 34 by 50 microns. 



Most of these giant cells are of quite normal pyramidal type but not a 

 few are of irregular polymorphic shapes. The nucleus is large, vesicular 



