THE FISSURA HIPPOCAMPI 99 
In the medial wall contiguous to these structures lie the typical 
subcortical tissues. The most cephalad of these, the septum 
(fig. 18, Sept.), bulges into the cavity of the lateral ventricle. 
Dorsal:to the septum, lying between the sulcus limitans hippo- 
campi and the pars tenuis of the lamina terminalis, is the thin 
septum ependymale (fig. 18, Sept. epen.). Morphologically it 
differs in no respect, except in position, from the area intercalata 
(fig. 18, A. ant.) adjoining the tela chorioidea telencephali medii. 
The anterior limbs of the lateral choroid plexuses are continuous 
with the paraphyseal arch a short distance cephalad to the ante- 
rior limb of the paraphysis. 
The foramen interventriculare is barely visible from the medial 
surface. The growth of the midthalamic region, forward and 
medialward, has restricted its caudal boundary. Its floor is 
filled with the medial limb of the caudate nucleus. Its anterior 
boundary is limited by the dorsal region of the terminal plate. 
Its vault contains the paraphysis and the tela chorioidea tel- 
encephali medii. Hence the boundaries of the foramen have 
not changed, although its diameter is narrower than that found 
in H 41. The surrounding structures have increased in size, 
growing toward the center of the foramen in all directions. 
Looking down toward the ventricular floor in the rostral 
pole of the hemisphere, at the level of the lamina terminalis, the 
anterior and the medial limbs of the caudate nucleus are seen. 
The medial nucleus increases in width gradually as far as the level 
of the anterior limb of the paraphyseal arch. From that point 
posteriorly it becomes narrower. The lateral nucleus of this 
complex springs from the side wall at the level of the root of the 
olfactory bulb. It attains its greatest width at the level of the 
dorsal portion of the lamina terminalis. Caudally it terminates 
in the region of the posterior extremity of the hippocampus. 
The angulus ventralis lies between the medial limb of the caudate 
complex and the lateral extension of the septal region. It extends 
from the base of the olfactory evagination into the floor of the 
foramen interventriculare. The two ventral sectors of the hemi- 
sphere wall have grown in length, so that the telencephalic 
evagination projects beyond the lamina terminalis much farther 
