148 JULIA WORTHINGTON. 
round body, embedded in the brain capsule, and very apt to 
be torn away in dissecting out the brain. It will be described 
later. 
The habenular ganglia.—These ganglia, though asym- 
metrical in form, are alike in structure. Their cells are 
smaller than those of any other part of the brain, but are 
similar to the two kinds already described. They are pressed 
close together throughout the ganglia, without definite 
grouping, and with their long axes running in nearly every 
direction. ‘There are a good many more of the light staining 
cells in the ventral parts of the ganglia than in the dorsal. 
In addition to the cells there are great strands of fibres, the 
beginnings and ends respectively of the great fibre tracts 
that centre here. Most of these fibres belong to the tractus 
olfacto-habenularis. The fibres of this tract come from 
all over the dorsal half of the olfactory lobes, and gather 
into thick strands—one for each lobe,—at the cando-mesial 
angle of the lobes. Running in this way through the cephalo- 
mesial parts of the fore brain lobes, they enter the habenular 
ganglia and cross in their ventral part, just caudad of the 
fore end of the right ganglion, in angles of from 45° to 90°, 
thus forming the habenular commissure. Across the caudal 
part of the ganglia run the fine fibres of the posterior 
commissure. 
The tracts of the habenular ganglia, in addition to the 
tractus olfacto-habenularis, are the tractus habe- 
nulo-tectalis, and the bundles of Meynert. The fibres of 
the tractus habenulo-tectalis arise in the dorsal part of 
the ganglia. Some of them cross immediately to the oppo- 
site ganglion, others remain with the tract leaving the 
ganglion of their own side. The tracts are unsymmetrically 
placed in the ganglia, but are symmetrically placed in regard 
to the rest of the brain, the left tract leaving the left 
ganglion just before its caudal end, and the right tract being 
directly opposite to it. The tracts run ventrally in a slight 
caudo-laterad direction for about 1} mm., then turn sharply 
laterad, though still keeping a slight caudal direction, and 
