A CASE OF CYCLOPIA 229 



otherwise is characterized by subnormal development. As will 

 be subsequently noted in a future communication, there are 

 reasons for regarding this thickening in some areas as being also 

 partly due to hyperplasia. 



Under normal circumstances Bolton (2) has pointed out that 

 the cells in the cortex of the term child are less crowded than 

 are those in the cortex of the developing foetus. As an important 

 factor in reducing this aggregation of cells he points to the in- 

 creased superficial area of the cortex at term due to the maturing 

 convolutional pattern, ''and the consequent smaller number of 

 cells in a section of the same thickness." 



Bolton and Moyes (3) have shown that the first large well 

 developed cells in the cortex are the Betz cells and that these are 

 prominent as early as the eighteenth week of foetal life. They 

 are situated in the basal portion of the inner fiber layer. These 

 authors also express an opinion that the sensory or afferent 

 fibers to the cortex are in all probability developed before the 

 motor or efferent fibers from the cortex. 



In this case it has been shown that in those areas reached by 

 the thalamic fibers, there is a marked tendency toward atypical 

 overgrowth in certain neurones of the superficial layers with 

 which these fibers come in contact. The presence of afferent 

 fibers thus influences the growth of cortical neurones. Ordinarily 

 these afferent fibers must enter through the basal portion of the 

 cortex. It is in this basal portion of the cortex that the first 

 well differentiated neurones appear and it is the basal laminae 

 of the cortex that are the first to be evolved. It would be 

 interesting to determine how far the tardy ontogenetic devel- 

 opment obtaining over some areas of the normal cortex were 

 dependent upon the late appearance in these areas of afferent 

 projection fibers. 



Naegeli (17) has described numerous well developed pyramidal 

 cells in the cortex in his case, which have attained a considerable 

 degree of differentiation and are possessed of short axone pro- 

 cesses but which do not come into relation with any projection 

 fibers from the thalamus, none of which, he says, gained the 

 cerebrum. He has termed this growth process 'self-differentia- 



THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 23, NO. 3 



