378 ELIZABETH CAROLINE CROSBY 
basal olfactory and non-olfactory correlation areas are well de- 
veloped, as in reptiles, that true hippocampal cortex begins to 
appear. 
Johnston has emphasized the fact that the hippocampus is 
an olfacto-visceral center, although in a later paper (’15, p. 412) 
he has said that there are olfacto-visceral correlations in the subic- 
ulum as well. It is well to notice that these types of nervous 
impulses are not first assembled in the hippocampus. On the 
other hand, this cortex simply brings together material already 
correlated, partly in the hypothalamus and more completely 
within the basal telencephalic centers. Three types of centers 
concerned with olfactory impulses are represented then within 
the hemisphere. 
1. Those basal centers concerned with the distribution of ol- 
factory impulses and their summation and correlation among 
themselves. 
2. Those basal centers concerned with the correlation of 
olfactory and non-olfactory impulses. 
3. Those centers which receive impulses from correlation cen- 
ters of the second type or from similar non-olfactory correlation 
centers and integrate these impulses. This integration of ma- 
terial already correlated is characteristic of the reptilian cortex. 
Into the hippocampus come impulses from the parolfactory area 
and the tuberculum olfactorium on the one hand, and from the 
pyriform lobe cortex by way of the alveus on the other hand. 
In Amphibia (Herrick, 710) the primordium hippocampi oc- 
cupies the dorso-medial portion of the medial wall of the hemi- 
sphere. This region has all the characteristic fiber tracts of the 
hippocampus (cf. Herrick, ’10, p. 480) but there is no differen- 
tiated cortex in this region except possibly to a small degree in 
Anura, where there is a row of cells close to the surface of the 
ventro-medial wall which send out wide spreading dendritic 
processes among the incoming fibers and which resemble in cell 
characteristics those cells found in the alligator at the anterior 
end of the hippocampal formation. 
In lower reptiles the dorso-medial area begins to form true 
hippocampal cortex. In the turtle, although, as has already been 
