220 : RALPH EDWARD SHELDON 
The medial forebrain bundle first appears rostrally at the level 
of the anterior commissure, on either side of the mid-line. Im- 
mediately dorsal to the commissural fibers appears the tractus 
hypothalamo-olfactorius medialis, made up largely of fine, medul- 
lated fibers, between which are found many unmedullated in 
character (fig. 37). All of the fibers of this bundle are ascending, 
originating in the nucleus posterior tuberis (figs. 102, 104). Part 
of them decussate almost immediately, as shown in fig. 102, while 
the majority pass up on the same side to decussate in the anterior 
commissure, closely associated with the fibers of the commissura 
hippocampi, pars posterior and commissura dorsalis. Both sets 
of fibers terminate in the corpus precommissurale, largely in the 
pars supracommissuralis. This tract is that observed by Gold- 
stein caudally, and called by him a descending tract. 
Ventral to the fibers of the anterior commissure, at its level, 
may be seen another component of the median forebrain bundle, 
the tractus olfacto-thalamicus, pars ventralis (figs. 36, 37). The 
fibers making up this bundle appear very similar to those of the 
tractus hypothalamo-olfactorius medialis. They originate from 
the corpus precommissurale, largely in the pars supracommis- 
suralis, and run caudo-ventrad, in a diffuse bundle, to terminate 
in the nucleus rotundus and the nucleus posterior thalami. 
At the caudal margin of the anterior commissure a third com- 
ponent, the tractus olfacto-thalamicus, pars dorsalis, appears. 
This is a rather diffuse bundle, made up of fine medullated and 
intermingled unmedullated fibers, which originate largely in the 
supracommissural part of the precommissural body and terminate 
in the nucleus subrotundus. This bundle, together with the pars 
ventralis, was noted by Goldstein, rostrally (Taf. 11, fig. 7). 
He points out that one passes dorsal and one ventral to the tractus 
olfactorius medialis, pars lateralis, and that both originate in the 
medial olfactory nucleus. Apparently, however, he failed to 
follow all the fibers caudad, as in the more caudal region he ob- 
served only the tractus hypothalamo-olfactorius medialis, which 
tract he had not seen farther rostrally. The two parts of the 
tractus olfacto-thalamicus form the tractus olfacto-hypothalami- 
