OLFACTORY CENTERS IN TELEOSTS 203 
Ventrally of the nucleus rotundus, extending caudo-laterally 
from the level-of the nucleus posterior tuberis, to the level of the 
caudal margin of the corpus mammillare, lies the nucleus subro- 
tundus (figs. 106, 117). 
When the three components of the nucleus are considered to- 
gether, it is noted that the nucleus prerotundus forms a cap over 
the rostro-mesal surface of the nucleus rotundus (fig. 84), decreas- 
ing in transverse diameter as the latter increases in size (fig. 89). 
At approximately the level where the nucleus prerotundus ends, 
the nucleus subrotundus is beginning to appear, embedded in the 
nucleus rotundus ventro-laterally (fig. 106). Further caudally 
(fig. 117), since the nucleus rotundus extends caudo-mesally 
while the nucleus subrotundus extends caudo-laterally, the two 
come to lie approximately in the same horizontal plane, one lateral 
to the other, the nucleus rotundus merging into the dorsal margin 
of the corpus mammillare; the nucleus subrotundus’ similarly 
ending in the nucleus cerebellaris hypothalami and losing its 
typical shape and appearance (see figs. 136-140, for a horizontal 
projection of these nuclei). 
In addition to their conspicuous size, the nuclei rotundi show 
a characteristic structure, hardly fully brought out in any of the 
drawings. The nucleus prerotundus throughout most of its 
extent is composed of rather large scattered cells, together with 
small numbers of various smaller sized cells (fig. 85) showing 
faintly between them. Severalof thecells from Golgi preparations 
are shown in figs. 86 to 88. The cells of the nucleus rotundus 
are smaller and more nearly of the same size. They are always 
scattered in groups or islands, giving a characteristic appearance 
to the nucleus (fig. 90). Figs. 91 to 94 show several from Golgi 
preparations. The nucleus prerotundus and rotundus combined 
form the ‘kleinzellige’ portion of the nucleus ventralis thalami of 
Goldstein. The most easily recognizable of these nuclei is the 
nucleus subrotundus, owing to its extremely characteristic appear- 
ance near its rostral end, or head. There, as shown in figs. 106 and 
107, it presents a circular appearance in transection, with its cells 
grouped in the center and surrounded by a clear peripheral area. 
The cells average larger than those of the remaining two nuclei 
