CRANIAL NERVES OF SILURUS AND MORMYRUS 25 
important nucleus in the vestibular apparatus is the nucleus 
ventralis (fig. 7, N.v.) of Kappers?! and Wallenberg,” described 
by Cajal?3 and Tello™ under the name of tangential nucleus. 
This nucleus is an important motor reflex center for the vestib- 
ular root [see for fibers ending in it, fig. 11 (9c) and for those 
originating from it, fig. 7]. It is, however, also traversed by 
fibers (fig. 7) which run more latero-mesad, apparently accom- 
panied by fibers originating from the cells of the nucleus which 
also run in a dorso-medial direction, taking their caudal course 
beneath the fibrae arcuatae internae [fig. 11 (9 b)]. 
In addition to these fibers the first vestibular root forms also 
a descending system, the spinal vestibular fibers [fig. 11 (12)]- 
More caudally these fibers run along the ventro-lateral pe- 
riphery of the bulb, between the secondary VII tract and the 
nervus lateralis posterior. They keep this position during their 
caudal course, successively joining the fibers of the posterior lateral 
nerve (fig. 10, s. VIII"). 
Besides pee spinal VIII fibers there are others which de- 
scend beneath the lobus lateralis anterior [fig. 11 (10)] and still 
others which descend first in the peripheral part of the bulb and 
then are pushed mesially by the descending system that con- 
stitutes the second (caudal) vestibular root [fig. 11 (11)]. These 
fibers first run beneath the lobus lateralis posterior, but finally 
take their course beneath the lobus lateralis anterior (the latter 
part of their course not being indicated on my scheme (fig. 11). 
The second vestibular root consists chiefly of descending 
fibers [fig. 11 (13)] which run through and terminate in the lobus 
lineae lateralis. I have not been able to see any ascending fibers 
of this root. In the more caudal levels, consequently, three de- 
scending vestibular tracts are found under the lobus lineae 
lateralis anterioris, one lying medially coming from the anterior 
21'The structure of the teleostean and selachian brain. Jour. Comp. Neur., 
vol. 16, 1906. 
22 Toc. cit., Anat. Anz., Bd. 31, 1907. 
23 Sur un noyau special du nerf vestibulaire des poissons et des oiseaux. Tra- 
vaux du laboratoire de recherches biologiques, fasc. 1 and 2, 1908. 
24 Loc. cit., Trabajos, tomo 7, 1909, pp. 14 and 9. 
