THE AMYGDALA IN AMPHIBIA 263 
then, is the physiological primordium of the amygdala, but this 
nucleus as a morphological entity has not emerged from the com- 
mon olfacto-striatal matrix. In the Anura, on the other hand, 
there is such a nucleus amygdalae with all of the characteristic 
connections enumerated above. 
V. THE COMPARATIVE ANATOMY OF THE STRIO-AMYGDALOID 
COMPLEX 
Returning now to the Anura, we find the lateral wall of the 
hemisphere considerably more highly organized. The dorso- 
lateral quadrant has assumed definite form as lateral olfactory 
nucleus anteriorly and pyriform lobe posteriorly, much as in 
lower mammals. It is sharply separated from the underlying 
ventrolateral quadrant by external and ventricular sulci and 
between these a histologically defined zona limitans lateralis. 
The fiber connections are as in urodeles, though more clearly 
defined. 
In the ventrolateral quadrant at the rostral end immediately 
behind the olfactory bulb there is an undifferentiated region 
which may receive some secondary olfactory fibers, though 
our preparations do not reveal them. Behind this is a true 
corpus striatum, characterized by connection with the lateral 
forebrain bundle with no olfactory component. ‘This striatal 
region is enlarged at the level of the interventricular foramen. 
Closely associated with it, but structurally distinct, is a true 
amygdala not related to the lateral forebrain bundle, which is 
characterized by: 1) a specific ventrolateral olfactory tract from 
the vomeronasal formation of the olfactory bulb; 2) a specific 
relation with both ascending and descending hypothalamic fibers 
of the olfactory projection tracts; 3) a habenular connection 
through the stria medullaris; 4) a dorsal connection with the 
septum and preoptic nucleus through the stria terminalis; 5) a 
ventral septal connection through the diagonal band of Broca; 
6) a specific commissural connection with the opposite amygdala; 
7) a connection with the overlying pyriform lobe through the 
tractus amygdalo-pyriformis. 
