360 J. B. JOHNSTON 
The fibers which enter the rostral end of the primordium hippo- 
campi from the formatio bulbaris are of course part of the olfactory 
tract. In the previous description (’02a, p. 40) it was stated that 
these come chiefly from the opposite side, crossing in the olfactory 
decussation. The contribution of the commissure to the fiber 
bundle entering the primordium hippocamp? is illustrated in figure 
24. Further study, both of the preparations used at that time 
and of new preparations, has shown, however, that a much larger 
number of direct fibers are present than was previously thought. 
These fibers are soon mingled with the fibers of the first and second 
bundles of the stria medullaris mentioned above and can not be 
distinguished with certainty. It is clear, however, that many 
fibers which enter from in front break up into end branches in 
the primordium hippocampi. Since we know of no other animals 
in which olfactory tract fibers run without relay to the nucleus 
habenulae, the presumption is strong that these olfactory tract 
fibers end in the primordium hippocampi. This is the more prob- 
able in view of the fact that in selachians corresponding fibers are 
present which end in the primordium hippocampi in part on the 
same side and in part after crossing inacommissure situated above 
the neuroporic recess. 
Schilling and Tretjakoff both state that the fibers of the tractus 
olfacto-habenularis give collaterals to the ‘praethalamus.’ Such . 
endings would represent a rudimentary tractus olfacto-corticalis. 
On comparative grounds the presumption is strong that those 
fibers mentioned above which run up form the medial olfactory 
nucleus rostral to the interventricular foramen to enter the pzim- 
ordium hippocampi must constitute a tractus olfacto-corticalis. 
The efferent tract from the primordium hippocampi has thus 
far been very imperfectly understood. The writer described fibers 
descending to the ‘striatum’ and these have been confirmed by 
Tretjakoff. These fibers are fine and do not appear in sufficient 
numbers in my preparations to warrant the conclusion that they 
represent the chief or only efferent path of this highly differen- 
tiated nucleus. Neither is it clear that they end in the ‘striatum’. 
It is possible that they pass through the ‘striatum’ but are not 
impregnated beyond. Other fibers may descend in the tractus 
pallii, as this tract in selachians and ganoids contains descending 
