THE AMYGDALA IN AMPHIBIA 273 
end in the distribution area of the dorsolateral olfactory tract. 
It is true that the telencephalic distribution of these thalamic pro- 
jection fibers in mammals is typically neopallial, and these fibers 
might be regarded as neopallial in the Amphibia if only there 
were any neopallium here. The fact is that they reach an area 
which is dominated by the lateral olfactory tract and which con- 
tinues to be so dominated even in mammals where it develops 
true cortex of the pyriform lobe. 
The process of the gradual unfolding of the neopallial cortex 
under the combined influence of functional factors primitively 
present in the paleostriatum and pyriform lobe has been briefly 
sketched by Elliot Smith (’19) and need not be reviewed here; 
but it is interesting to note that during the entire course of this 
evolutionary history the cortex of the pyriform lobe retains a 
very primitive character and even in the highest mammals is 
structurally and physiologically transitional, on the one hand to 
the subcortical lateral olfactory nucleus and on the other hand 
to the subcortical corpus striatum and the amygdala. In high- 
er brains the neopallial components of this undifferentiated com- 
plex as seen in Amphibia have passed on to more elaborate evo- 
lution elsewhere, but the corpus striatum (or part of it) and the 
pyriform lobe remain as residual structures in practically their 
primitive relationships. 
In this confusing region it is very difficult to determine where 
are the limits between cortical and subcortical structures. In 
fact, the terms cortex and pallium are currently employed so 
loosely that such a determination is impossible without a more 
satisfactory definition of these terms than has hitherto been 
published. A clear reformulation of these concepts in the light 
of recent comparative and embryological studies is urgently 
needed. 
The amygdala of the frog is clearly subpallial in the sense that 
Gaupp (’99) and I (10) have defined the pallium; in accordance 
with the same criteria, the greater part, at least, of the mamma- 
lian amygdala appears to be pallial. But careful embryological 
work will be required before the mammalian complex can be re- 
solved. If Iam correct in my belief that the amphibian amygdala 
