THE FISSURA HIPPOCAMPI 119 
younger to older stages so far as studied. The area chorioidea 
is differentiated early into two regions, one of whose lateral 
limbs becomes the thin lamina epithelialis of the lateral plexus 
and the other an area in which changes are insignificant. The 
former is the paraphyseal arch and the latter is the tela chorioidea 
telencephali medii. 
In table 4 the writer has attempted to measure, somewhat 
crudely to be sure, two dimensions of these midline structures. 
The total lengths of the telencephalon medium were taken by 
TABLE 4 
Measurements of divisions of the telencephalon medium 
TELENCE- TELA CHORIOIDEA 
EMBRYO PHALON | LAMINA TERMINALIS TELENCEPHALI PARAPHYSIS 
MEDIUM MEDII 
Number | Length Length Length Paes Length Width Length Width 
mm mm. mm. mm. mm. mm. mm. mm. 
1121 | 11.8 | 2.388 | 0.944 | 0.054] 0.2481} 0.02 1.24 | 0.02 
940 | 14.0 | 1.620] 1.048!| 0.088 | 0.168! | 0.028 | 0.404] 0.032 
liege tO. Ve | 1:2.52 ed 72 O17 “1-02.29 0.03 0.51 | 0.04 
460 | 20.0 | 2.516 | 1.60 0.15 | 0.40 0.036 | 0.516 | 0.036 
HOt} 627.8: | 2.645 | 2.27 O51 70h 15 0.02 0.225 | 0.05 
H41 | 32.1 | 2.834] 2.40 | 0.644 | 0.184 | 0.041 | 0.25 | 0.064 
HA63)))| © 39.1. |, (3:24 -| 2.56 | 0.80 | 0:21 0.72 0.470 | 0.044 
886 | 43.0 | 3.384 | 2.94 | O73 O15 0.75 0.2 0.045 
i These are estimates, because the angulus terminalis is not present. 
measuring the distance between the recessus preopticus and the 
velum transversum at the magnification of the model studied. 
That length was then divided by the magnification. Conse- 
quently, the figures are approximately the actual length in 
millimeters as found in the particular embryo and therefore 
comparative. 
The distribution of the increase lies entirely in the lamina 
terminalis. The telencephalon medium grows in length mainly 
because the lamina terminalis increases in length. If the ac- 
companying figures 1 to 6 be examined, especially figures 3 to 
6 sketch 1 and 1d, through the ventral and dorsal divisions of the 
