CRANIAL NERVES OF SILURUS AND MORMYRUS 19 
[X and also join the spinal V tract—a striking example of func- 
tional arrangement of fiber systems on account of their correlated 
function. 
The spino-occipital column in Silurus is, like that of all other 
fishes, the direct continuation of the cervical gray matter, and 
it reaches rather far ventrally. Its frontal extremity extends 
less far forward than in several other teleosts. 
Since this cell column exhibits the greatest frontal extension 
in those fishes where the tectum opticum is large and the ventral 
tecto-bulbar reflex paths are considerably developed, it may be 
that the smaller degree of this frontal extension in Silurus is a 
result of the small optic system of this animal. 
A striking feature in the brain of this animal is the considerable 
development of the lateralis system, which I shall treat now to- 
gether with the vestibular system. 
Examining sections of the oblongata of Silurus in the caudo- 
frontal direction, one is struck by the great development of the 
crista cerebellaris which covers the massively developed dorso- 
lateral region of the bulb. At its most caudal level there is only 
one rather small crista, lying between the nervus lateralis poste- 
rior and the lobus sensibilis [IX + X (fig. 10). 
Some sections more frontally, where the posterior lateral nerve 
has penetrated into the bulb, another crista is added to this, 
remaining independent from it and located more laterally. 
Proceeding in the frontal direction, we find that the crista of 
the nervus lateralis posterior (this is the one that is added) grows 
much larger than the crista of the lobus nervi lateralis ante- 
rioris (the one that reaches most caudally) and pushes it more and 
more medially (fig.-9). In the rostral levels of the bulb the 
lobus nervi lateralis posterioris is about three or four times larger 
(fig. 6) than the lobus nervi lateralis anterioris, which is not 
surprising on account of the enormous size of the body of Silurus 
andthe great number of lateral line organs. 
Proceeding still farther forward, we find that the lobus nervi 
lateralis posterioris first acquires a connection with the cerebellum 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 25, No. l 
