216 RALPH EDWARD SHELDON 
from the nucleus preopticus, pars parvocellularis anterior, to 
join the main ,tract (figs. 73, 141, 142), termed the tractus pre- 
optico-habenularis, pars anterior. Where the nucleus intermedius 
becomes continuous with the nucleus posthabenularis, it gives off 
a few unmedullated fibers to the tractus olfacto-habenularis, the 
tractus intermedio-habenularis, pars posterior (figs. 141, 142). 
The pars magnocellularis gives rise to two sets of fibers for the 
habenulae, both unmedullated, a diffuse fiber connection extend- 
ing dorsad, close to the median ventricle, the tractus preoptico- 
habenularis, pars medialis (fig. 73), and a small compact tract, 
which passes lateral to the basal forebrain bundle, the tractus 
preoptico-habenularis, pars lateralis (figs. 74, 141, 142). Further 
caudally tracts join the main bundle from the pars parvocellu- 
laris, pars posterior, of the nucleus preopticus, the tractus pre- 
optico-habenularis, pars posterior; and from the nucleus post- 
habenularis, the tractus posthabenulo-habenularis (figs. 141, 142). 
Part of this may also be descending and, therefore, homologous 
with the tractus habenulo-thalamicus of Herrick. 
All of these fibers make up the tractus olfacto-habenularis. 
It will be noted that the only medullated bundle is the tractus 
teniae; this is likewise the most conspicuous of the different fiber 
systems which probably explains why it is the only one previ- 
ously described in teleosts. The habenular ganglia, then, receive 
fibers from practically all parts of the caudal portions of both the 
lateral and medial olfactory columns. Laterally, fibers pass up 
from the nucleus teniae of the lobus pyriformis, medially from the 
nucleus preopticus, nucleus intermedius, nucleus entopeduncularis 
and nucleus posthabenularis. The lateral connection is the one 
observed by Edinger, Catois, Kappers, Goldstein, ete., while the 
medial is that found chiefly in Acipenser and Petromyzon by 
Johnston. Apparently the largest bundle in Petromyzon cor- 
responds with the tractus preoptico-habenularis, pars lateralis, 
in the carp. 
Practically all of the fibers of the tractus olfacto-habenularis 
decussate in the commissura habenularis, the commissura superior 
of many writers (figs. 76, 141, 142). It is possible that a few fibers 
end on the same side. It is likewise possible that there are a few 
