THE FISSURA HIPPOCAMPI 91 
_is the fissura hippocampi (see groove, fig. 15) and coincides in 
extent with the stippled area in figure 16. 
The greatest change in the di-telencephalon relationship is 
the ventricular growth in the medial limb of the corpus striatum 
(figs. 15, 29, and 32). Looking into the cavity of the telencephalic 
vesicle, several typical markings may be seen. In the latero- 
ventral sector lies a depression, which divides the nucleus caudatus 
into a medial and lateral limb. The lateral hillock is a small 
and insignificant ventricular ridge; the medial, much larger than 
the lateral, lies in the ventro-medial part of the ventral sector, 
just lateral to a deep groove which separates the corpus striatum 
from the septal region. This medial limb of the corpus striatum 
is most evident from the ventricular aspect of the di-telence- 
phalic union. The septal region which composes the ventral 
portion of the medial wall ventral to the angulus terminalis and 
anterior to the lamina terminalis is separated from this portion 
of the corpus striatum by a deep groove, called by Herrick (710) 
in Amblystoma and other vertebrates the angulus ventralis 
(fig. 31, Ang. ven.). Further dorsalward in the medial wall of 
the hemisphere a slight ventricular ridge can be followed, from 
the base of the beginning olfactory evagination to the caudal 
pole. This is the hillock made on the ventricular surface by 
the fissura hippocampi. This ridge is limited ventrally by a 
sharp turn in the tissue wall, a deep, well-marked sulcus, which 
will be called the sulcus limitans hippocampi (figs. 16, 29 to 
31, Sul. vent.). Ventral to this sulcus and caudal to the anterior 
limb of the paraphyseal arch lies the massive choroid invagina- 
tion. Rostral to this portion of the paraphyseal arch, the medial 
wall ventral to the sulcus limitans hippocampi is very thin epithe- 
lial tissue, the area epithelialis (figs. 16, 31, A. ep.). 
The outer contour of the telencephalic vesicle is undergoing 
a change, marked not only by growth rostral to the lamina termi- 
nalis region, but also now by a seeming swing of the most dorsal 
portion of the outer di-telencephalic junction caudo-ventrally. 
This junction liés ventral to the dorsal thalamic suleus, which 
divides the midthalamus from its dorsal region. This relation- 
ship of the diencephalon to the telencephalon upon the outer 
