THE FISSURA HIPPOCAMPI Lim 
tion, but caudal to the lamina the greatest depth, of this fissure 
shifts toward the sulcus limitans hippocampi (compare Fis. hip. 
in figs. 33 and 34 with the fissure in figs. 35 to 37). The depth 
of the fissure, then, is found in the center of the future hippocam- 
pus at those levels in which its ventral limb is continuous with 
the septum itself; when, however, its ventral limb is joined to 
the thin septum ependymale or the taenia fornicis, the depth of 
the fissure shifts ventrally. 
Within the septum ependymale is now found a thin marginal 
velum (fig. 35). There is no change in the area intercalata. 
However, in the lamina epithelialis, the portion which extends 
to the paraphyseal arch (fig. 36) approaches the cuboidal epithe- 
lium of much older stages while that portion contiguous to the 
outer limb of the velum transversum is as primitive as the whole 
of the area in the 19.1-mm. embryo. 
The primordium of the fascia dentata extends from a region 
anterior and dorsal to the angulus terminalis almost to the tip 
of the temporal pole, opposite the suleus limitans hippocampi 
(cross-hatched area, fig. 17). In figure 33 (Fas. den.) it lies as 
a small well-defined group of cells in the marginal velum below 
the fissura hippocampi (fig. 33, Fas. hip.). Here, as well as in 
the next figure (fig. 34, Fas. den.), these cells seem to be continuous 
with the nucleus of the septum, the nucleus medialis septi (Nuc. 
med. sept.). This nucleus always appears ventral to the suleus 
limitans hippocampi and can be identified easily in the next 
level pictured, through the septum ependymale (fig. 35, Sept. 
epen.). Here also the fascia dentata is well marked. In the 
last two levels presented this structure maintains its initial 
relationship to the sulcus limitans hippocampi and the fissura 
hippocampi (figs. 36 and 37). 
The first three figures (figs. 33 to 35), when compared with 
those of the 14-mm., are excellent illustrations of the shifting of 
the hippocampal primordium to the midmedial region of the 
cerebral hemisphere. The whole dorsal lateral wall and almost 
half of the dorso-medial, at this stage, are composed of neopallium. 
But within the ventro-lateral sector bounded by the sulcus 
above the lateral limb of the caudate complex and the angulus 
