CELL MASSES IN THE FOREBRAIN 411 
and the cell-free zone, which accurately marks the boundary 
of the lobe, meets the surface ventral to the sulcus endorhinalis. 
This sulcus is therefore actually within the area of the pyriform 
lobe. At the caudal border of the striatal area the band of small 
cells along the ventral border of the pyriform lobe spreads ven- 
trad in a broad sheet across the base of the amygdaloid fissure 
(fig. 5) and expands into a large nucleus of small cells occupying 
the lateral and rostral part of the amygdaloid prominence (figs. 
17, 16). This sheet of small cells is accompanied by a large 
bundle of fibers from the lateral olfactory tract which ends in 
this nucleus. This is the nucleus of the lateral olfactory tract 
(digs. 3, A7). 
A further examination of the relations of the small cells in the 
pyriform lobe shows that essentially two nuclei or two cell groups 
are to be distinguished. The small cells in the region of the 
amygdaloid fissure are very clearly separated from the large- 
celled part of the lobe by a space or cell-free zone (figs. 15, 16, 17). 
Farther forward although there is no space separating them, 
the small cells do not mingle with the large cells and the small- 
celled band becomes continuous with the superficial layer of the 
tuberculum and through that with the medial olfactory nucleus 
(fig. 26). The large-celled nucleus, on the other hand, main- 
tains its identity rostrad to the peduncle as already described 
(fig. 28). Moreover, the location of the small cells below the 
endorhinal sulcus gains significance from the fact that at the 
level of the tuberculum the small-celled band spreads ventrally 
to become continuous with the superficial layer of the tuberculum. 
The cell-free zone which limits the pyriform lobe internally now 
becomes continuous with the limiting zone which appears between 
the caudate sulcus and the layers of the tuberculum (figs. 26, 27). 
These relations when summed up with the description that has 
gone before show that there is a continuous area of small-celled 
olfactory nuclei comprising the medial parolfactory nucleus, the 
superficial layer of the tuberculum, the small-celled band of the 
pyriform lobe, the small-celled nucleus of the amygdaloid complex 
and the nucleus of the diagonal band. These together constitute 
a continuous ring which surrounds the crucial-striatal area. 
