368 D. DAVIDSON BLACK 



more especially of the inner cell stratum, with the resulting for- 

 mation of atypical laminae, together with a greatly increased total 

 thickness of a cortex made up of closely crowded poorly differen- 

 tiated cells. This latter condition is evidently associated with the 

 hyperplasia which is, in general, opposed to specialisation. 



It is of interest to note that in tissues of mesodermal origin 

 lacking trophic control, somewhat similar phenomena have been 

 shown to occur. Cehanovic (4) has demonstrated that the re- 

 moval of trophic control in the vascular system, is accompanied, 

 more especially in arteries, by a marked hypertrophy and hyper- 

 plasia of muscular and connective tissue elements in the media 

 and also of the elements of the intima. 



SUMMARY 



The points illustrated by the condition of cortical development 

 in this case may be summarized as follows : 



1. When afferent projection fibers are present in abnormal 

 locations, their presence may result in atypical growth and differ- 

 entiation of neurones which are usually characterised by the 

 regularity of their form and their small size. 



2. The presence of these afferent fibers apparently provides 

 the necessary stimulus toward differentiation required by the 

 large efferent neurones. Furthermore the elaboration and dif- 

 ferentiation of the primary outer cell lamina of the cortex is 

 dependent upon the establishment of the normal functional 

 connections of these two units. 



3. When the normal trophic stimulus provided by the afferent 

 projection fibers in the cortex is lacking, there results an atypical 

 cortical development which may be compared to the hyperplasia 

 occurring in many tissues of mesodermal origin in the absence of 

 their trophic control. 



4. The cell lamination resulting from the disturbance of affer- 

 ent connections is atypical and characteristic of the case. It is 

 thus fruitless to attempt to identify accurately by means of the 

 lamination pattern, any cortical area in a case such as this with 

 the histologically different areas in the normal cortex. 



