No. 1.] AMPHIBIAN BRAIN STUDIES. 81 
sural fibres, decussational fibres are intermingled. I have 
myself discovered that in the upper bundle or corpus callosum 
of Menobranchus there enter fibres from the diencephalon. 
Proteus agrees with JMenobranchus in the entire separation of 
this bundle from the anterior commissure. I have seen no trace 
in the Amphibia of the fornix columns which I have found 
in the Ophidia (86, p. 533, Fig. 20), and Bellonci has figured in 
the Lacertilia, (87). 
Other important commissures are the infundibular com- 
missures which connect the infundibular lobes, dorsally and 
ventrally, and the extensive commissure of the tectum opticum. 
THE ORIGIN OF THE Optic NERVES. 
It has recently occurred to me that the presence of the 
two whitish bands seen upon the external dorsal surface of the 
optic lobes in many of the Uvodela is partly due to the under- 
lying optic tracts. It is certain that these tracts in the Uvodela 
are principally confined to the median portions of the tectum 
opticum. They can be followed as far forwards as the cerebel- 
lum, II. ¢ 1, Figs. 23, 24, and descend obliquely from this region 
to the nerve. In the Uvode/a there is no differentiation of cells 
into distinct layers. 
The character of the cells of this region is shown in Fig. 
25a, which illustrates an interesting observation upon the ap- 
parent connection of the fibres either of the optic nerve or 
of the direct sensory mesencephalic tract with the fibres of 
the descending Trigeminus tract. The peripheral cells of the 
central gray substance, II. x, have long single processes. 
These processes branch, one of the finer branches en- 
tering the coarse fibres of the descending Trigeminus, the 
other passing outwards into the fine layer of fibres of the 
tectum opticum. This observation has been confirmed at 
several points. It shows first that the fibres of the Trigemi- 
nus may have a compound origin, partly from the large cells, 
5, partly from the small cells; second, that here is a possi- 
ble centre between the optic and trigeminus nerves. 
The second optic tract, II. #2, arises from a mass of cells im- 
the complete structure of these commissures. I do not therefore at present feel in 
a position to reply to his courteous criticism of my paper. 
