CELL MASSES IN THE FOREBRAIN 405 
(figs. 17, 16) the lentiform nucleus becomes covered externally 
by a layer of small cells which reaches from the pyriform lobe to 
the amygdaloid complex and will be described below as the nu- 
cleus of the lateral olfactory tract. The lentiform nucleus now 
decreases in volume caudally, contains several dense collections , 
of cells which are closely related to the thickened ependyma of 
the middle groove (figs. 16, 33), becomes less rich in cells and 
finally merges with the central core of the dorsal ventricular ridge 
behind the end of the middle groove (fig.14). 
Throughout its whole length the lentiform nucleus is sharply 
delimited from the pyriform lobe and (except at its caudal end) 
from the dorsal ventricular ridge, by cell-free zones. It is marked 
off from the caudate only by arather sudden change from large 
to small cells. The thickened ependyma covering its surface is 
sometimes separated from that covering the caudate by a slight, 
sharp groove. 
Among the fascicles of the internal capsule which come ‘rom 
the sensory bundle of the crus (see later section on the pallium), 
are found many cells conspicuously larger than the ordinary 
cells of the lentiform nucleus. The position of these is indicated 
in figures 18 and 19. They may prove of importance in further 
comparisons with the mammalian brain. | 
TUBERCULUM OLFACTORIUM 
The tuberculum consists of a cap of two layers of cells covering 
the basal surface of the caudate nucleus at its rostral end (fig. 27). 
The outer layer is sparsely filled with small cells and is closely 
related at its medial border with the medial parolfactory nucleus 
and at its lateral border with the pyriform lobe at the sulcus 
endorhinalis (figs. 26, 27). The inner layer has larger cells and 
is characterized by the grouping into islands which have been 
described by Calleja and Cajal. These islands are for the most 
part clusters of the large cells of the deep layer. They contain 
from four or five to many cells, which present no regularity of 
arrangement. The cell bodies are pear-shaped or stellate and 
are largely filled by vesicular nuclei with prominent nucleoli. 
In these respects they do not differ materially from the cells 
