A CASE OF CYCLOPIA 223 



sue was not in a favorable condition for metallic impregnation 

 and, although numerous attempts were made, no successful prepa- 

 rations were obtained. 



Everywhere in this case the cortex is markedly thickened. 

 The thickest cortex at birth (at least in the case I have used as 

 control) is over the central area. Here the cortex is about 2 mm. 

 in thickness, while the thinnest cortex in the cyclopian foetus meas- 

 ures 3 mm. or more, the line of demarcation between cortex 

 and medulla being very indefinite. The thickening is mostly 

 the result of an increase in the deep polymorphic layer of cells, 

 although all layers show an increased thickness. 



When examined at a low magnification the wall of the cerebrum 

 is everywhere seen to be divisible roughly into five strata. This 

 lamination is illustrated somewhat diagramatically in figure 18. 

 The strata appear as follows: (1) an outer layer comparatively 

 free from cells and varying in thickness in different areas, (2) a 

 stratum rich in cells but whose elements tend to become arranged 

 in arge irregular groups (3) a layer of densely packed cells, (4) 

 a layer whose cellular elements resemble somewhat in arrange- 

 ment those of the second stratum, and (5) a layer representing 

 the medullary center. 



For a more detailed description, sections have been selected 

 from two histologically distinct areas of the cortex (figs. 15 and 

 16). Figure 17 shows a section through the precentral area in 

 a normal full term foetus for comparison as to thickness and gen- 

 eral arrangement of elements. These drawings were made with 

 the aid of a Leitz projectoscope and are each at a magnifi- 

 cation of 65 diameters. 



Figure 15 has already been referred to and is a section taken 

 through the cortex near the junction of the thalamus and cere- 

 bral vesicle. The plexiform layer (I) at its periphery shows an 

 irregular layer of embryonic, or more probably neuroglia, ele- 

 ments. Into this plexiform layer stream thalamic fibers. The 

 boundary between layer (I) and the next stratum (II) is not 

 sharp. In the second stratum (II) occur the groups of large 

 polymorphic elements mentioned above. The third layer (III) 

 is made up of medium and small pyramidal cells and embryonic 

 elements. It is slightly thicker than layers I and II combined 



