AN ATYPICAL CEREBRAL CORTEX 365 



distinct. The occurrence of well differentiated elements superfi- 

 cial to the latter layer is the exception rather than the rule over 

 this area. In the deeper strata of the inner cell layer there occur 

 either singly or in groups, numerous giant polymorphic or pyra- 

 midal cells. The smaller polymorphic elements at this level show 

 a greater degree of differentiation than those at higher levels. 

 Practically all the thalamic fibers reaching this area of the cortex 

 course in the medullary center and enter the deep layers of the 

 cortex first with the result noted. 



If the hypothesis put forward in an earlier paper (2) to account 

 for the form of the forebrain vesicle, in this case be carried to a 

 logical conclusion in detail, it will be noted that the area border- 

 ing upon the divergent limbs of the Y-shaped median furrow 

 would correspond in general to the Rolandic area in the normal 

 cortex. I mention this only on account of the curious coinci- 

 dence of the presence of a well marked series of giant cells in the 

 deeper cell strata in this area and regard it as a coincidence only. 



Regions destitute of thalamic fibers 



Areas 1 A and 1 B represent the type of lamination character- 

 istic of those areas quite destitute of the influence of thalamic 

 projection fibers. These two areas, though wide apart, show 

 essentially similar types of lamination. The only real difference 

 in their structure lies in the fact that, as Area 1 B is nearer the 

 cortical limbus, the cortex as a whole is much the thinner of the 

 two. It is over these areas that cell differentiation is found to be 

 least in evidence, while the total number of elements is consider- 

 ably greater in a given section in these areas than in those reached 

 by thalamic fibers in abundance. 



It is to be noted that despite the close crowding of cells alluded 

 to above, the total thickness of the cortex in Area 1 A is greater 

 than that found in any other area except those in the immediate 

 neighborhood of entering thalamic fibers. In the latter areas the 

 great thickness is at least in part due to the scattered arrange- 

 ment of the cells resulting from the influence of the presence of 

 these atypical fibers. Thus I am led to conclude that, whatever 



