THE FOREBRAIN OF THE ALLIGATOR 313 
6. Tractus olfacto-habenularis posterior. This tract arises 
near the posterior end of the hemisphere from the nucleus of 
the lateral olfactory tract and the ventro-medial nucleus in the 
region illustrated in figure 12. It passes directly dorsalward 
into the stria medullaris. 
Olfactory projection tracts 
The entire secondary olfactory area is broadly connected with 
the hypothalamus by way of the medial forebrain bundle. De- 
scending impulses are carried from the medial (septal) wall of 
the hemisphere through the tractus parolfacto-hypothalamicus 
(tr. septo-hypothalamicus of some other authors), as described 
beyond in the account of the medial forebrain bundle. The 
connections between the olfactory centers in the lateral wall. of 
the hemisphere and the hypothalamus may in the aggregate 
be termed the olfactory projection tracts, following the usage of 
Ramon y Cajal. The application of the term projection tracts 
to these fibers finds its justification in the intimate relation be- 
tween the secondary or basal olfactory centers and the olfactory 
cortex of the pyriform lobe in the lateral wall. 
There are two of these tracts which enter respectively the 
ventral and the dorsal sides of the medial forebrain bundle (figs. 19 
and 20), which together probably correspond approximately with 
the so-called tractus pallii of fishes and amphibians. 
Ventral olfactory projection tract (figs. 16 to 19). This tract 
has already been mentioned in our account of the anterior di- 
vision of the lateral cortico-habenular tract. It arises from cells 
of the pyriform lobe and the nucleus of the lateral olfactory 
tract. It runs with the anterior division of the lateral cortico- 
habenular tract until it reaches the ventral part of the medial 
forebrain bundle, which latter it accompanies caudad. It 
- probably ends in the hypothalamus. 
Olfactory projection tract of Cajal (figs. 19 to 21). The fibers 
of this olfactory projection tract pass directly dorsalward from 
the ventro-medial nucleus, then curve medialward and _ pass 
caudad lying dorsally of the forebrain bundles and between them 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 27, NO. 3 
