FOREBRAIN MORPHOLOGY 419 
29), and it is here impossible to make a well-justified subdivision 
of these parts. But a closer examination shows that in the lateral 
brain-wall, basal to the sulcus limitans externus, there is a broad 
band of the brain-wall, where the ventricular layer is relatively 
thin (figs. 30 to 32, n.olf.l.), much thinner than in the basal part 
of the vesicle. This part corresponds to what Elliot Smith has 
called ‘striatum.’ Really this part (figs. 30 to 32) projects a 
little into the lateral ventricle so as to suggest a ‘striatum,’ but 
there are no special structures proving that it is really a striatum. 
I will call this part the lateral olfactory nucleus, although it corre- 
sponds probably to both this nucleus and a ‘striatal’ swelling 
in selachians. 
The basal portion of the lateral ventricle is covered with a very 
thick ventricular cell-layer (figs. 29, 30, t.olf.). In the caudal 
third of the forebrain, the superficial portion of this layer is 
delaminated from the ventricle as to form a somewhat cortical, 
free cell-lamina encircling in transverse sections in the shape of a 
U the basal portion of the ventricle (figs. 31, 32, t.olf.). This 
cell-lamina is the cortex of the tuberculum olfactorium, as pointed 
out by Elliot Smith. This cortex, thus, is free from the ventricle 
in its caudal portion, but the rostral portion is always ventricular. 
Rostrally it is confluent with the ventricular cell-layer at the 
frontal pole of the brain. 
The caudal margin of the tuberculum olfactorium cortex pro- 
jects into a cellular process, representing a nucleus taeniae (figs. 
33, 34, n.t.), so interpreted also by Elliot Smith. This process 
is pierced by small bundles belonging to the lateral forebrain 
bundle, as is also the rest of the tuberculum olfactorium cortex in 
this region of the brain. 
The subpallial septum is divided into two parts, a rostral and a 
caudal. These are separated by a heavily ependymated sulcus 
septalis (figs. 29 to 33, ss.) as in selachians. This sulcus begins 
at the ventromedial corner of the ventricle about the middle of 
the forebrain (fig. 29) and goes from here obliquely upward to 
end at the foramen monroi a good way beneath the sulcus limitans 
medialis (fig. 33). The portion of the subpallial septum included 
in transverse sections between this sulcus and the sulcus septalis is 
