A CASE OF CYCLOPIA 231 



relation exists between the development of the corpus striatum 

 when present, and such efferent neurones as those under dis- 

 cussion. 



One other point may here be noted in connection with the 

 examination of this cortex. It has been found that the character 

 of the lamination, the thickness of the cortex and the condition 

 of cell development, vary in different regions. Two of these 

 histologically distinct areas are illustrated in the figures. It 

 would seem that these areas are not sharply marked off from 

 each other but are separated by transitional zones. However, 

 as no complete topographical survey was made, this point was 

 not definitely determined. Thus, histologically distinct areas 

 are present but, with the exception of the dentate and fimbrio- 

 dentate fissures, there is a complete absence of true sulci. This, 

 then, is further evidence, it would seem, of the truth which Bolton 

 has pointed out, namely, that the development of the convolu- 

 tional pattern is secondary to the differentiation of the cortex into 

 histologically distinct areas. 



Cerebral limhi. At the base of the inner pillar of the thick- 

 ened recurved margin of the cerebral vesicle, the thin roof be- 

 comes attached to the edge of the cortex. The relations of the 

 roof in this region have already been noted in the gross descrip- 

 tion (hgs. 11 to 13). Sections were made at intervals along this 

 margin and the relations of the cerebral limbi studied. Drawings 

 of three of these sections are here reproduced. Figure 18 is a 

 section taken in the mid-sagittal plane; figure 19 is a section 

 taken at the junction of the anteror and middle thirds, and 

 figure 20 a section at the junction of the middle and posterior 

 thirds of the left cerebral margin. The outlines of these drawings 

 were made with the aid of a Leitz projectoscope and at the same 

 time lines were drawn marking off the various cell laminae of 

 the cortex. The spaces between these lines were subsequently 

 shaded in free hand, so the details of cell arrangement are only 

 indicated in a somewhat diagrammatic fashion. However, the 

 relative thickness of the cortex and the arrangement of its vari- 

 ous strata, as seen under low magnification, are fairly accurately 

 shown. 



