364 D. DAVIDSON BLACK 



cialisation at birth, that is, the outer cell layer of the cortex, to 

 develop to a marked degree and become more highly differentiated 

 than most of the elements at deeper levels. 



The deepest stratum of the cortex in this area is also reached by 

 thalamic fibers by way of the medullary center. This is the path 

 along which these fibers pass under normal circiunstances. In 

 the deep cell strata there also occur very numerous large and 

 medium sized well differentiated cells, and in addition in Area 

 5, giant cells are to be found here. The area of least differentia- 

 tion occupies an intermediate position between the zonal and the 

 polymorphic layers, and is the level least accessible to thalamic 

 fibers. 



Projection fibers entering mainly via medullary center 



Passing on to the consideration of those areas reached by thal- 

 amic fibers mainly by way of the medullary center, it will be 

 noted that the cell lamination approaches more closely the gener- 

 alized type already described. 



In Area 3, from the central portion of the base of the left pos- 

 terior lobe, there are still certain thalamic fibers present in the 

 zonal layer. As has been shown, irregular, quite large, multi- 

 polar elements are of frequent occurrence here either in the zonal 

 layer or at irregular intervals throughout the second stratum. 

 Layer III is here recognized for the first time as a lamina sparsely 

 beset with small cells and dividing the cortex into an upper and 

 a lower cell stratum. In the deeper cell strata the elements show 

 quite an advahced state of differentiation and numerous medium 

 and large pyramidal and polymorphic cells are found here. These 

 deep strata are in closest relation to the thalamic fibers coursing 

 in the medullary center and are evidently stimulated by this 

 contiguity. 



In Area 2, practically no thalamic fibers course in the zonal 

 layer, yet here and there in the outer part of Layer II medium 

 sized multipolar elements are to be found. The cell lamination 

 in this region is more distinct than in Area 3 and the line of demar- 

 cation between Layers I and II is quite sharp. Layer III is also 



