116 MARION HINES 
side of the arch are the rostral evagination of the roof of the 
third ventricle, the postvelar tubules of Warren (P. vel. t.). How- 
ever, in the midline above the arch there are two small tubules 
whose continuity with the membranous roof is found anterior 
to the velum transversum. They form a real pouch which ex- 
tends forward over the telencephalic roof plate (fig. 18, Par. 
p.). This condition of the human paraphysis is strikingly like 
that figured by Warren (’17) in the 25-mm. embryo (figs. 14 and 
15). Rostral to the anterior limb of the paraphysis is the tela 
chorioidea telencephali medii. It is undifferentiated, a true 
epithelial tissue. The tissue, which joins it dorso-laterally, is 
separated into two layers, an inner matrix and an outer layer, 
which contains fibers, emerging from the hippocampus, the fornix 
(fig. 45, For.) 
In a section parallel with the length of the fissura hippocampi 
(fig. 46, Fis. hip.) the fascia dentata (fig. 46, Fas. den.) is a 
thin band of cells lying in the marginal layer of the hippocampus. 
This section cuts the sickle-shaped fissura hippocampi tangently 
so that the typical hippocampal structure may be seen at two 
ends. 
The 43-mm. embryo, Mall Collection, 886 (figs. 47 to 50) 
Orientation is difficult in this embryo, because it was cut 
eoronally to the long axis of the cerebral evagination. A com- 
parison of the levels from which the figures were taken with the 
median sagittal view (fig. 20) is illuminating. Figure 47 passes 
longitudinally through the rostro-dorsal extent of the fissura 
hippocampi. ‘The fascia dentata lies as a band in the outer 
margin (Fas. den.). The intermediate cell layer is well differ- 
entiated, while that of the pyramids extends only across the mar- 
gin of the hippocampus. Lying between the fascia dentata and 
the matrix are the developing fibers of the fornix system. 
Figure 48 was taken at a level farther caudally, below the 
dorsal arch of the fissura hippocampi. The architecture of the 
hippocampus is the same in its anterior and posterior extent 
with the exception that the number of developing fornix fibers 
is greater posteriorly. Following the posterior limb to its caudal 
