380 ELIZABETH CAROLINE CROSBY 
the medial forebrain bundle to reach the medial wall of the hemi- 
sphere carry mainly visceral impulses and the dominant, al- 
though not the only, type of correlation in this wall is prob- 
ably olfacto-visceral. 
Impulses of a like kind reach the pyriform lobe region from 
the hypothalamus by way of the ventral olfactory projection 
tract (figs. 16 to 19). Thus, this series of steps which seems to 
have lead to the development of the hippocampus, can no doubt 
be duplicated in the development of the cortex of the pyriform 
lobe through the interrelation existing between the hippocampal 
cortex and the pyriform lobe cortex on the one hand and the in- 
terrelation between that latter cortex and the amygdaloid com- 
plex on the other, although the details are not very well known. 
In Amphibia (Herrick, ’10) the dorso-lateral area of the hemi- 
sphere receives lateral olfactory tract fibers and presumably is 
the primordial material for the formation of pyriform lobe cortex 
and perhaps for part of the amygdaloid complex. Moreover, 
in Amphibia, the somatic area is ventro-lateral in position and 
receives and sends out fibers through the lateral forebrain bundle. 
In reptiles, this somatic area has increased in size because of the 
greater number of somatic fibers that it receives; for accompanying 
the telencephalic changes there has been an increased growth and 
differentiation of the thalamic regions, particularly of the lateral 
portions which receive the fibers of the incoming optic and leminis- 
cus systems. This differentiation of the lateral part of the 
thalamus (the neothalamus of Edinger) is correlated with an in- 
crease in the number of fibers sent forward into the hemisphere 
from this region. This increase in the incoming fibers has lead 
to a change in the nuclear pattern among reptiles as compared 
with the pattern found among Amphibia. Some of the for- 
ward extending somatic fibers have begun to pass dorsalward 
of the old limits of the striatum and in the turtle (Johnston, 15) 
and in the alligator, perhaps in other reptiles also, the dorsal part 
of the lateral wall is chiefly a somatic correlation center. The 
lateral and ventro-lateral portion of this dorsal wall, however, 
is occupied by the cortex of the pyriform lobe and the anterior 
part of the nucleus of the lateral olfactory tract. The main part 
