THE FOREBRAIN OF THE ALLIGATOR alo 
pyriform lobe and the nucleus of the lateral olfactory tract. 
These impulses come by way of the alveus which carr es impulses 
in both directions, as it does in higher forms. ‘The 'aterally di- 
rected dendrites receive short association fibers from the alveus 
and perhaps impulses from other ncoming fibers. 
The axones of the double pyramids are slender and run lateral- 
ward, dividing in many cases into two branches (fig. 36). One 
of these branches enters the alveus and can often be traced a long 
distance, although it has been impossible as yet to follow any 
single fiber all the way into the pyriformlobe. The second branch, 
when present, goes to the septum or enters one of the descending 
diencephalic tracts (the fornix or tractus cortico-habenularis). 
3. Small projection cells (figs. 32, 33). Besides the double 
pyramid cells there are other projection cells in the hippocampus. 
These are smaller than the ones just described and may be either 
pyramidal, oval or nearly round in form. They are usually 
either slightly lateral or slightly medial to the double pyramids 
and send their dendrites to both lateral and medial surfaces, where 
they receive the same sorts of impulses as are brought to the 
double pyramids. ‘The axones, like those of the latter, may 
divide into two branches (fig. 33), one entering the alveus and 
the other running ventralward into the septum and presumably, 
in some cases, entering tracts descending to the diencephalon. 
4. Small intrinsic cells (fig. 34). The dendrites of the double 
pyramid and small projection neurones form a thick feltwork 
on each side of the more deeply placed cell bodies. Scattered 
through this feltwork are cells of several types, only one type of 
which is shown in the figures, which send out relatively short 
bushy dendrites and receive collaterals from incoming fibers or 
from axones of the hippocampal projection cells and discharge 
back into the dendrites of the latter. In this way the whole 
of the hippocampus is tied up together and correlated and unified 
responses are made possible. Some of these cells are typical 
type II neurones, others have longer, less branched processes 
and short slender axones. Both of these sorts are apparently 
intrinsic to the hippocampus. 
