THE FOREBRAIN OF THE ALLIGATOR 349 
Functional complexes formed by the basal nuclei of the lateral 
wall. In the foregoing paragraphs, an account has been given 
of the relative positions and the extents of the various nuclei 
found in the lateral wall of the hemisphere, and something has - 
been said of their fiber connections. Two problems then arise, 
the first regarding the way in which these centers interact in 
the functioning brain of the alligator; the second regarding their 
phylogenetic significance as forerunners of centers found in mam- 
malian brains. 
Two types of nervous impulses enter the lateral wall of the 
cerebral hemisphere, (1) descending mpulses from the olfactory 
area, and (2) ascending somatic sensory impulses from the cen- 
ters of the thalamus. The nuclear pattern of this basa area 
of the forebrain has been determined in large measure by the 
distribution and mutual interconnections of the incoming fibers 
of these two systems. 
The first type of nervous impulse includes the secondary and 
tertiary fibers of the lateral olfactory tract, which, entering from 
in front, distribute to the nucleus of that tract throughout its 
entire extent and, turning gradually dorsalward, in the posterior 
half of the hemisphere distribute to the lateral portions of the 
dorso-lateral area. The lateral part of this dorso-lateral area, 
the nucleus of the lateral olfactory tract, and the ventro-medial 
nucleus all give rise to fibers of the stria medullaris and the 
first two masses (and in turtles the ventro-medial nucleus also) 
discharge through the stria terminalis. The ventro-medial nu- 
cleus in both the turtle and the alligator discharges into the 
diencephalon through the great olfactory projection tract of 
Cajal. . 
The identification of the amygdaloid complex of higher forms 
is based on the following features: 1) upon its reception of fibers 
from the lateral olfactory tract (figs. 16, 18); 2) upon its relation 
to the pyriform lobe cortex (figs. 7 to 10); 3) upon its giving rise 
to fibers of the stria terminalis (figs. 19 to 21—in this is included 
its connection with the opposite side of the brain by way of the 
anterior commissure) ; 4) upon its giving rise to fibers of the stria 
medullaris (figs. 16 to 21). It is evident that the group of centers 
