THE FISSURA HIPPOCAMPI 1341! 
continuous invagination of tissue which lay undifferentiated in 
the sickle-shaped telencephalic wall adjoining the di-telencephalic 
groove. There is no indication in the 11.8-mm. or in the 14- 
mm. embryo of an area peculiarly differentiated in that region. 
The primitive hippocampus arches over the caudal pole of the 
developing hemisphere. Since the hippocampal tissue precedes 
iN 
Undit fas. den. 
Primhip. 
Aint 
5 <a 
Tel ch. et 
Anglerm. 
Sept va 
Tubolf~ — Sept. 
Lamferm 
RECMCOD == 
Rec postop, 
Rec. int 
aso bol | | x 
Fig. 16 Outline sketch of the same brain as that shown in figure 15. The 
dotted line, continuous with the telencephalon above the diencephalic roof plate, 
indicates the most caudal boundary of the cerebral hemisphere. The planes of 
section of figures 29 to 32 are indicated. 
Post. LAyp. 
the choroid plexus in differentiation, it is natural to place the 
anlage of the plexus in the epithelial tissue which lies between the 
definitive hippocampus and the paraphyseal arch and velum 
transversum. ‘These two divisions of the lateral choroid plexus 
are fundamentally the same and their development coincides 
with the ventro-caudal growth of the hippocampus. The more 
extensive that growth is, the more extensive the so-called pos- 
