CRANIAL NERVES OF SILURUS AND MORMYRUS 9 
the nucleus are approximately the same, but in the caudal part 
the transverse dimension may be a trifle smaller. Directly 
behind the third nerve a considerable decussation of cerebellar 
fibers is found, as is the case in most teleosts. 
The trochlearis enters the brain near the transition from the 
tectum opticum to the cerebellum. Its fibers are not as thick 
as those of the III nerve. After having entered the brain, they 
first run in a medio-dorsal direction, bending slightly caudad. 
It is extremely difficult to trace the IV root in the intricate 
net-work of fiber systems found in this level of the brain and it 
may be that its course as indicated in my projection (fig. 4) needs 
correction. Its entrance, however, as well as the location of the 
nucleus, are not in doubt. 
The IV nucleus has a relatively lateral position under the floor 
of the ventricle and it is not connected with the III nucleus. 
- This separation of the III and IV nuclei occurs often in teleosts, 
but is not a constant feature. . 
Very striking in Silurus is the very frontal place of entrance 
of the IV root (fig. 4). In all the bony fishes as yet examined 
this root enters the brain on a level behind the nucleus (Tinea, 
-Cottus, Pleuronectidae, Gadus, Lophius).‘ Only once, in a holo- 
cephalic fish, Chimaera,® has such a frontal entrance of the IV 
root been found, its fibers here leaving the brain on a level with 
the oculomotor nucleus. This frontal displacement of the tro- 
chlearis entrance is most probably due to mechanical factors only. 
The trigeminus root in Silurus (fig. 5) is intimately connected 
at its entrance with the sensory VII root and the anterior lateralis 
root, as has already been observed by Stannius.* Similar con- 
ditions are described by C. J. Herrick’ in the North American 
‘siluroid fishes. Nevertheless, the motor and sensory V can be 
4 Kappers, Weitere Mitteilungen iiber Neurobiotaxis. No. VII. Folia Neuro- 
biologica, Sommer-Erginzungsheft, Bd. 6, 1912, figs. 24, 25, 29, 33, 34. 
° Kappers, Motor nuclei in the oblongata and midbrain of Chimaera monstrosa. 
Proc. kon. Akad. van Wetenschapp., Amsterdam, March 8, 1912, p. 1141. 
6 Stannius, Das periferische Nervensystem der Fische. Rostock, 1849, p. 21. 
7C, J. Herrick, The cranial nerves and cutaneous sense organs of the North 
American siluroid fishes. Jour. Comp. Neur., vol. 11, p. 183. This author also 
observes that the gasserian ganglion and ganglion geniculi are fused. 
