THE FISSURA HIPPOCAMPI 93 
In the telencephalon itself there is little change. The em- 
bryonic fissura hippocampi (lying in the stippled area, fig. 17) 
extends from the region dorsal to the olfactory bulb (fig. 17, 
Olf. bulb) to the tip of the temporal pole. The greatest differ- 
ence in the growth between this brain and that of the 19.1-mm. 
embryo is in the appearance of neopallium on the medial wall 
of the definitive occipital pole. 
In the floor of the lateral ventricle two hillocks lie side by 
side, separated by a shallow sulcus. The lateral hillock, much 
larger in this embryo than in H 178, is the lateral limb of the 
caudate complex. A sulcus separates the medial hillock (figs. 
17, 35, and 36, Cor. str. med.) from the thalamus. This groove 
runs up and over the floor of the foramen interventriculare and 
ends in the recessus preopticus (fig. 17, Rec. preop.). Rostral 
to the medial limb of the caudate complex and making up the 
ventro-medial portion of the cerebral hemisphere is the septum. 
This area is limited dorsally by the sulcus limitans hippocampi 
(fig. 17, Sul. vent.) and ventrally by the angulus ventralis (fig. 
30, Ang. vent.). The angulus ventralis is a shallow groove which 
lies between the septum and the rostral portion of the caudate 
nucleus. Its rostral end becomes lost in the evaginating olfactory 
bulb. The septum itself has increased in thickness by a marked 
ventricular growth. 
There are, then, three morphological differences to be noted 
in this brain as compared with that of H 173: 
1. Increase in the tissue forming the vault of the hemisphere. 
2. Growth of the lateral nucleus of the corpus striatum. 
3. Dorsal extension of the ventrally thickened portion of the 
septum. 
The 27.8-mm. embryo, University of Chicago, H 91 
The foramen interventriculare is no longer elliptical in out- 
line. It is a dorso-ventral slit lying beneath the paraphyseal 
arch. It is bounded posteriorly by the midthalamus, ventrally 
by the medial limb of the caudate complex, dorsally by the area 
chorioidea, and anteriorly by the lamina terminalis. The sulcus 
