384 ELIZABETH CAROLINE CROSBY 
responsible for the migration of the cells of the general pallium 
from their original ventricular position to form a more super- 
ficial cortical lamina, for their neurobiotactic influence (Kap- 
pers) would have this tendency. 
SUMMARY 
To recapitulate, it appears to us that the following factors are 
involved in giving the morphological form and typical functional 
activity of the alligator forebrain: 
1. This forebrain is very largely under the dominance of the 
olfactory system. 
2. Its differentiation into basal and cortical centers is due, 
directly or indirectly, to the entrance of non-olfactory dien- 
cephalic impulses. 
3. These diencephalic fibers are partly for synaptic relations 
with the olfactory fibers; and consequently basal centers for the 
correlation of olfactory and non-olfactory impulses are present. 
A variety in the type of the incoming diencephalic impulses has 
lead to the differentiation of a number of different basal nuclei, 
for it has not been the number of synapses through which an im- 
pulse has passed, nor the number of fibers coming into a nucleus, 
but the variety in the types of stimulation received which has 
lead to the differentiation of the telencephalic centers. 
4. In the lateral wall of the hemisphere the primordial striatum 
is present, which is practically free from olfactory influence and 
is under the influence of somatic fibers from the thalamus. The 
somatic area is larger than in lower forms and correlated with 
this increase in size is an increase in size and differentiation of 
the lateral part of the thalamus. 
5. There are three primordial cortical areas represented and 
they all have certain characteristics in common. All of these 
are primarily for the integration of impulses already correlated 
in the basal centers or transmitted to them by way of association 
fibers from the other cortical centers. A certain proportion of 
comparatively pure olfactory impulses enters the hippocampus 
and the pyriform lobe; but, as has already been discussed, these 
