679 
to the cephalic aspect of the prethalamus as defined in a recent 
article. The olfactory structure is strictly after the reptilian type. 
The pero (or mouth portion) is composed of the glomerulary struc- 
ture interspersed with irregular multipolar cells similar to those 
of the reptiles. The pes contains numerous small cells of the same 
form as those of the cerebrum. The radix lateralis springs from 
the pero and passes along the rhinalis fissure directly to a distinct 
lobus hippocampi. This portion of the axial lobe is distinct topo- 
graphically and histologically from the remainder. Its cells are 
smaller and of two sorts; the first being small flask cells, the second 
irregular densely stained pyramide resembling what the writer has 
Fig. 3. A similar section of the same brain at the crura olfactorii. The entire 
length of the radix lateralis is seen in the single section. A small descending fornix 
tract is seen emerging from the corpus fornicis. 
All the figures were drawn with the aid of a camera lucida, the left side being 
diagramatic. 
called rhinomorphic cells in higher vertebrates. The radix late- 
ralis enters the hippocampal lobe peripherally and the entire tract 
can be seen in a single horizontal section. The radix mesalis springs 
from the central or pes portion of the olfactory and passes caudad 
and then dorso-mesad to decussate in a special (ventral) portion of 
the anterior commissure. The praecommissura proper contains decus- 
sating tracts from the thalamus. 
