948 
MR, A. SANDERS ON THE ANATOMY OE THE 
is directed obliquely backward from its ganglion to its exit, whereas in ordinary Teleostei 
it passes directly downward ; I speak here of course in reference to the position which 
these animals habitually assume. The commissura ansulata consists of the same two 
divisions as in M. cephalus, but the parts which it connects are slightly different. 
It derives its lateral fibres from the base cf the wings to which it acts as a commissure ; 
the upper part of its decussating bundles, instead of going to the torus semicircularis 
as in M. cephalus , goes into and is lost in the granular layer of the anterior end of 
the cerebellum. Upon further consideration I find that the homology which I gave 
for this commissure in the brain of M. cephalus was most probably wrong, and the fact 
that some of its fibres in this animal are derived from the cerebellum seems to confirm 
its determination, as the pons varolii, which was also adopted by Fbitsch.* 
The posterior commissure (fig. 3) occupies its usual position behind the third ventricle 
and the infundibulum, but here it is more isolated, for the posterior wall of the infundi¬ 
bulum appears to be wanting, so that the fissure in the floor of the aqueduct of Sylvius 
communicates with it without any partition ; it forms a communication between regions 
corresponding to those united by this commissure in M. cephalus. 
The anterior end of the dorsal commissure of the tecta (figs. 2 and 3) is all that 
remains of that commissure which in Teleostei generally extends for the whole length 
of those bodies. This is placed immediately above the posterior commissure and even 
extends in front of it; this relation contributes material for forming an opinion as to 
the homology of the tecta, which will be touched upon presently. 
The deep transverse commissure, and with it the nucleus rotundus, have completely 
disappeared in this family, and have left not a trace behind. 
Deep Origins of the Cranial Nerves. 
In the Mormyridce all the nerves can be easily found except the trochleares and the 
abducentes ; these, probably from the great degradation of the muscles of the eyeball, 
have become reduced to such extreme minuteness as readily to escape detection. 
The optic nerves, although of small size, present, at their entrance into the optic 
tract, a true chiasma nervorum opticorum, formed by bundles which decussate, and at 
the same time form a felt-like structure. The optic tract, at its entrance, forms a 
thick layer of fibres surrounding the trigonum fissum and the hypoarium on three sides 
(figs. 2 and 3). I am sorry to have to differ from Bellonci t as to the origin of the 
optic nerve. The family of the Mormyridce present rather good subjects for investiga¬ 
ting the derivations of this nerve, as the tecta have been pressed forward and down¬ 
ward, so as to be placed immediately above the exit of the nerve in question, and 
consequently the optic tract passes directly upward into the tecta. I find that I cannot 
subscribe to the opinion that these latter bodies form the only origin of the optic nerves ; 
on the contrary, some fibres are distinctly seen to emerge from the inferior part of the 
trigonum fissum and from the region containing the small cells which line the infun- 
* Log. at., p. 74, fig. 44, p.v. t -^oc. c/it. 
