THE FISSURA HIPPOCAMPI 107 
or dorso-lateral olfactory areas, with the striatal complex, a 
condition comparable with that of the adult reptile (Crosby, 
717). Because of this confusion and the absence of neopallium 
in the amphibian, the writer prefers the use of sector stead of 
quadrant. Accordingly, in this brain each hemisphere can be 
divided into four sectors: dorso-lateral (neopallium), dorso- 
medial (primordium hippocampi), ventro-lateral (combined stria- 
tum, lateral olfactory area and pyriform lobe), and ventro- 
medial (septum and medial olfactory area). At this particular 
level the two dorsal sectors are of approximately the same thick- 
ness; the wall of the ventro-lateral sector, however, 1s much 
thicker than that of the ventro-medial. The dorso-medial sector 
may be distinguished from the dorso-lateral by a broad white 
marginal velum within the medial one (fig. 26, Prim. hip.). 
_ This same layer of the telencephalic wall within the dorso-lateral 
quadrant contains many neuroblasts (fig. 26, Neopal.). The 
matrix or zona ependymalis of the medial sector is not as broad 
as that of the lateral. The dorso-medial region is separated 
from the ventro-medial by a sharp ventricular groove, the sulcus 
limitans hippocampi of Herrick (fig. 26, Sul. vent.). The ventro- 
medial sector itself is divided into two histologically distinct areas: 
a dorsal! thin layer of tissue whose cells, packed closely together, 
show no definite arrangement, the septum ependymale (fig. 26, 
Sept. epen.), and a ventral whose thick wall presents an inner 
dense matrix and an outer zone, containing a few neuroblasts, 
the septum (fig. 26, Sept.). The two ventral sectors are separated 
from each other by a slight indentation in the ventricular surface 
the angulus ventralis (compare Herrick, ’10, figs. 13 and 14, 
A. V. with fig. 26, Ang. vent.). Lateral to the ventral angle 
the brain wall bulges into the ventricle, the first evidence of the 
corpus striatum, specifically, the medial nucleus of the caudate 
complex. Between this nucleus and the dorso-lateral sector must 
lie the future lateral olfactory complex and the lateral limb of 
of the caudate nucleus. The four sectors of the hemisphere are 
then, 1) the dorso-lateral or the neopallium; 2) the dorso-medial 
or hippocampal primordium; 3) the ventro-medial or the septum 
and the septum ependymale, and, 4) the ventro-lateral or the 
