128 MARION HINES 
tissue and approaches the extent of the differentiation in the hemi- 
sphere wall termed the primordial hippocampus (figs. 8 and 24). 
The interpretation of the further development of this tissue must 
be correlated with this finding, as well as with the facts of its 
phylogenetic development. 
This region of generalized morphology and fe stalons was 
divided for descriptive purposes into three areas, entirely upon the 
Fig.13 Medial sagittal view of the model of brain no. 940,14 mm. X 16}. 
basis of their respective destinies, namely, the septum ependymale, 
the area intercalata, and the lamina epithelialis. The relative 
growth of the septum ependymale may be seen at a glance by 
comparing the sections marked /d in figures 3 to 5. This region, 
an undifferentiated epithelium in the brains of the first four 
embryos described, begins to show a marginal velum in the 20- 
mm. embryo, which persists and grows in width in the brains 
of this group. The differentiation proceeds towards the angulus 
