OLFACTORY CENTERS IN TELEOSTS | 201 
(1) Epithalamus. The epithalamus of the carp is easily defined, 
consisting of the saccus dorsalis and epiphysis and the habenular 
centers, including the two habenular ganglia, the habenular decus- 
sation, or commissure and the nucleus posthabenularis, together 
with their connections. 
The ganglia habenularum are very conspicuous in the carp, 
protruding for half their diameter into the median cavity (figs. 
78, 81). Their cells are small and evenly distributed but thrown 
into groups or islands by the fibers of the tractus olfacto-habenu- 
laris and the fasciculus retroflexus (figs. 78, 81). As seen in Golgi 
preparations, the cells are very characteristic, of the type normal 
throughout the vetebrate series (fig. 75). 
Nucleus posthabenularis. Immediately ventral to the habenu- 
lar ganglia, the cells of the one continuous with the cells of the 
other, les the nucleus posthabenularis, ‘das posthabenulare 
Zwischenhirngebiet’ of Goldstein, the ‘posthabenulare Zwisch- 
enhirngegend’ of Bela Haller, Meynert’s nucleus of reptiles 
(figs. 78, 81). Rostrally, it becomes continuous with the nucleus 
intermedius (fig. 70), while caudally it extends beyond the level 
of the commissura posterior (fig. 84) always holding a position close 
to the median ventricle and ventral to the fasciculus retroflexus. 
(2) Thalamus. At the level of the habenulae, there appear on 
either side, immediately ventral to the arch of the tectum, the 
corpora geniculata lateralia. Mesal to the lateral geniculate 
body les the nucleus anterior thalami of Goldstein (figs. 78, 81). 
This is easily recognized, owing to its large size and its character- 
istic appearance, showing a ring of cells about its periphery (fig. 
81). 
Nucleus rotundus and associated centers. One of the most 
important. parts of the thalamus, and at the same time one of the 
most difficult to understand in all its relations, is the region of 
the nucleus rotundus. Owing to its prominence, it has been noted 
by nearly every writer on the teleostean brain. It was described 
by Fritsch and called by him the nucleus rotundus; Bellonci used 
the same term, while C. L. Herrick termed it the nucleus ruber. 
Goldstein assigns the name nucleus ventralis thalami to this 
