80 OSBORN. [Vot. II. 
cells behind this nucleus; third, to the tectum opticum. As 
it descends, the fibres divide into two bundles (Fig. 25), 
of which the anterior surrounds the superior processes of 
the ganglion cells of the oculo-motor nucleus (Fig. 20, pcs): 
this connection is so close that some of these fibres seem to 
be actually continuous with the cells. The posterior bundle 
has a similar connection with the cell processes of the pale 
ganglion, which may in fact also belong to the oculo-motor 
nerve. None of the fibres of this commissure can be traced 
directly into the main (sensory) tracts adjoining these nuclei, 
as observed by Pawlowsky, although such a connection seems 
highly probable (tractus cruciatus tegmenti). Dor- 
sally, the fibres of this commissure in Rana can be clearly 
followed into the peripheral white substance of the tectum 
opticum, as shown in horizontal sections. 
The Superior Commissure. This is much less constant 
in size and development than the foregoing. It is extremely 
small in the Azwra and apparently so in the Proteida,! but is 
large in Cryptobranchus and Amphiuma. It divides into two 
distinct bundles, one of which descends into the inner mantle 
of the hemispheres, secs, and finally disappears, after bending 
around into the outer portion of the mantle. The second bundle 
descends directly along the outer wall of the thalami. These 
bundles are clearly seen where the commissure is well developed, 
and I have fully described them elsewhere (84, p. 268, Fig. 8). 
One fact militates against our considering the commissure as a 
purely decussational system ; that is, the bundle entering the 
hemispheres is much larger than that entering the thalami. It 
forms either partly a commissural system between the poste- 
rior portions of the hemispheres and between the thalami, or 
partly a decussational system between the hemispheres and 
thalami. 
Cerebral Commissures. I have seen reason to partly 
alter my views as to the nature of the commissures of the 
hemispheres which were described in detail in my paper on 
the corpus callosum. The more recent researches of Bellonci, 
with the aid of the Golgi method, upon these commissures, 
should be consulted.2- They show that with the purely commis- 
1 Necturus. 
21 regret that I have not the opportunity at present to investigate thoroughly the 
interesting questions which Bellonci has raised in this valuable memoir in regard to 
