122 MARION HINES 
I 
commissure has grown across the midline. The bed for these 
fibers is laid down long before the fibers themselves appear. 
Further, the growth is appositional, taking place ventral to the 
center of the main body of the terminal plate and progressing 
both dorsally and ventrally. The most marked growth is found 
in the former region, and not in the vicinity of the angulus ter- 
minalis or the recessus preopticus. 
There is no constant change in the non-plexiform portion of the 
area chorioidea and if the structures adjoining this region are 
examined (figs. 1 to 6, sketch 2) they appear to be constant. 
J+ 
+ 
we = ; 
es 
i v\ i 
x. VE 
Figs.1to6 These are pen sketches of the midregion of transverse sections of 
the telencephalon, showing the position of cell groups in the tissue; they were 
drawn either from photographs of the sections or from projections made with the 
Edinger apparatus. 
Fig.1 The 11.8-mm. embryo, no. 1121, Mall Collection. X 25 
Fig.2 The 14.0-mm. embryo, no. 940, Mall Collection. X 25 
Fig.3 The 19.1-mm embryo, H 173, University of Chicago. X 163. 
