230 D. DAVIDSON BLACK 



tion/ as opposed to 'dependent differentiation/ using the terms 

 suggested, as, he says, by Roux (19). 



In this case, in some of the more basal portions of the cortex 

 which are lacking in medullated fibers of thalamic origin, there 

 are found in the deeper strata numerous giant pyramidal ele- 

 ments. These cells are much larger than any similar elements to 

 be found in the normal new-born cortex, and each possesses a 

 large vesicular nucleus with well developed karyosomes, while 

 in the cytoplasm Nissl bodies are well formed and prominent. 

 Although no medullated fibers of thalamic origin could be made 

 out in such sections, it is very doubtful if these large elements 

 can be considered as cells showing only 'self-differentiation;' they 

 are probably influenced by non-medullated afferent fibers. On 

 the other hand, in areas quite removed from possible thalamic in- 

 fluence as for example, the anterior portion of the rim of the cere- 

 bral cup, the smaller, more numerous and generally under-devel- 

 oped elements, making up the thickness of the cortex may, I think, 

 be classed as 'self -differentiated,' in the sense of Roux. 



The giant cells referred to in the preceding paragraph, which 

 are located in the deep cell lamina of the cortex, are strikingly 

 like the large efferent perikaryons described as Betz cells in the 

 normal cortex of mammals. It has been shown by Bolton (3) 

 that in the evolution of the cortex, those laminae situated above 

 the level of the Betz cells, are the site of greatest differentiation 

 and growth in the higher mammals and man. It thus happens 

 that the increased cortical thickness causes these large efferent 

 cells to lie more deeply in the human cortex than in that of lower 

 forms. If then the giant cells in this cyclopian cortex represent 

 the cell bodies of potential efferent neurones of the Betz type, the 

 location at such a cortical level would be a further argument 

 against any theory of phylogenetic reversion. An accurate 

 knowledge of the number, arrangement and distribution of these 

 cells would aid in determining how far such a comparison as 

 the above is justified. In the event of the presence of sufficiently 

 differentiated cortical tissue in any of the other cases of cyclopia 

 at present in my possession, a complete topographical survey of 

 such will be made. It would also be of interest to note what 



