290 J. B. JOHNSTON 
inus to the tuberculum olfactorium, which serves as a correla- 
tion center for oral and nasal sensory impulses (muzzle-sense). 
If this were the function of the tuberculum olfactorium, one 
would expect that in forms like man, in which the olfactory ap- 
paratus is reduced and the oral sense is very important, the tu- 
bercle would be large relative to the other olfactory centers. 
Such is not the case. On the other hand the forms in which the 
tuberculum is large are those in which the olfactory apparatus is 
very large (Ornithorhynchus, Didelphys, dog). 
There is more reason for comparing this with the descending 
bundle mentioned by Edinger (1908, pp. 123, 286) as arising in 
the lobus parolfactorius and running through the dorso-lateral 
part of the oblongata, to the cervical cord, tractus fronto-bul- 
baris. Edinger’s lobus parolfactorius is a large, illy defined 
region ‘‘which includes the whole base of the brain” (p. 252), 
and there is nothing to indicate from what part of this area the 
tractus fronto-bulbaris arises. Also, it seems fairly certain that 
the bundle above described ends largely or wholly at the level 
of the isthmus. It is quite possible that some of its fibers pass 
on to the cervical cord and that these constitute the tractus 
fronto-bulbaris of Edinger. 
Figures 2 to 6 show another bundle of considerable interest 
which is clearly defined in this series. This is the bundle of 
precommissural fornix fibers which enter the hypothalamus 
(fasc. praecom. pars hyp.). These constitute the most compact 
bundle in the system of vertical fibers in the ‘‘septum”’ rostral 
to the anterior commissure (fig. 2). The bundle is conspicuous 
in the sections back to the level of the optic tract, which it 
crosses to enter the lateral wall of the tuber cinereum. Whether 
the fibers reach the mammillary body can not be determined in 
this specimen. 
