A CASE OF CYCLOPIA 

 Th. 



237 



Fig. 21 A Medial sagittal section of a His' model of the brain at the end of 

 the fourth week (modified from Spalteholz). C.st., corpus striatum; 1st., isthmus; 

 Mes., mesencephalon; Met., metencephalon; Myel., myelencephalon; Pal., pal- 

 lium; P.m.th., pars mamillaris hypothalami: P.o.th., pars optica hypothalami; 

 Rh., rhinencephalon; S.Lim., sulcus limitans; Th., thalamus. 



Fig. 21 B Right half of a His' model of the brain at end of fourth week, from 

 which the anlagen of the rhinencephalon, corpus striatum, pars optica and pars 

 mamillaris hypothalami have been removed. The cut edges are lined. 



Fig. 22 Model resulting from the approximation of the cut surfaces as indi- 

 cated in the text. -T.c, taenia cerebri; T.th., taenia thalami; X, marks the line 

 of union between the original ventro-mes'ial edges of pallial anlagen. Other 

 letters as in figure 21A. 



