OLFACTORY CENTERS IN TELEOSTS 197 
centers, and morphologically related to a part, at least, of the cor- 
pus striatum of higher forms. 
(e) Nucleus commissuralis lateralis. Situated in the ventro- 
medial portion of each basal lobe, in the region of the anterior 
commissure, at either end of the commissure is a small compact 
nucleus of fairly large, closely packed cells (figs. 38, 56). No 
references to it in the literature have been noted; it has, therefore, 
beens termed the nucleus commissuralis lateralis, owing to its 
location, laterally at the level of the anterior commissure. 
(f) Nucleus preopticus. Immediately caudal to the anterior 
commissure there appears ventrally the recessus preopticus of the 
third ventricle (fig. 56). Surrounding this, on either side, and 
passing rostrally insensibly into the pars supracommissuralis, 
is the nucleus preopticus. This nucleus is composed of cells of 
two types; at the level of the caudal margin of the hemispheres is a 
dense mass of cells bordering the median ventricle; its cells are some 
of the largest in the brain (fig. 71), and are flask-shaped with their 
bases directed toward the ventricle and most of their processes 
extending laterally and ventro-laterally (figs. 67, 70,71). This is 
here termed the pars magnocellularis of the nucleus preopticus. 
Rostral to this nucleus, continuous with the pars supracommis- 
suralis, is a nucleus of small cells (fig. 64). This group of cells 
extends caudally, lateral to the pars magnocellularis, gradually 
curving around it caudally, thus enclosing the nucleus magnocel- 
lularis on three sides. In contradistinction to the nucleus mag- 
nocellularis this is called the pars parvocellularis of the nucleus 
preopticus. To the portions rostral, lateral and caudal to the 
pars magnocellularis are assigned the suffixes, anterior, lateralis 
and posterior, respectively (figs. 64, 66, 67, 70, 78). This nucleus 
extends caudally to the region of the fibrae ansulatae. 
In Golgi preparations the pars parvocellularis shows cells of 
several types, resembling closely the various kinds of small cells 
of the corpus precommissurale. 
The nucleus preopticus was recognized by C. L. Herrick in 1892. 
Herrick saw both the large and small cells and applied the name 
nidulus praeopticus to the larger portion of the nucleus; it is 
probable, however, that his nucleus postopticus contains a por- 
