680 
The method employed consisted in the preparation of an unbroken 
series of sections, cut in three planes, horizontal, transverse and ver- 
tical to the long axis of the brain. 
The brains of these urodeles seem to differ chiefly from those of 
the Batrachia in the adult retention of the straight tubular condition 
so characteristic of the embryo. The batrachian brain has undergone 
a fore and aft shortening and with this arises the greater lateral exten- 
sion of all its parts, also the following points of contrast. 1) In the Frog 
the iter is folded backwards into a double cavity by a sigmoid curva- 
ture of the loof; in the above Urodeles this ventricle is a straight tube. 
2) In the Frog the anterior commissure, as a part of the lamina termi- 
nalis, forms the anterior boundary of the unpaired cerebral cavity ; in 
these Urodeles this commissure is in the brain floor some distance be- 
hind the lamina terminalis proper. Other variations are simple reflec- 
tions of the varying proportions of the peripheral organs. 
1) The fibre courses composing the main system pass through the 
pars peduncularis of the mesencephalon, through the lower portions 
of the thalami and enter:the basal portions of the hemispheres. This 
system is reinforced by fibres descending from the central cell masses 
both of the optic lobes and optic thalami; these fibres descend ob- 
liquely forwards and backwards from each of these bodies. The main 
system also receives a large bundle of fibres from each of the lobes 
lying at the sides of the infundibulum. Part of the fibres of the main 
system enter the hemispheres direct, part can be traced into the lower 
portion of the anterior commissure to enter the opposite hemisphere. 
The lower portion of this commissure is simply a decussation system. 
Finally, oblique fibres, not part of the main system, connect the he- 
mispheres and optic thalami directly. 
2) The anterior commissure consists of the decussation 
system, above mentioned, also, as observed by Stieda?, of an upper 
course of fibres connecting the upper mesial walls of the hemispheres. 
In Menobranchus this upper course seems to be completely separated 
from the lower course and traverses the ventriculus communis 
as a distinct commissure which might readily be mistaken for the 
middle commissure. The fibres of the posterior commissure, as 
observed in the chick by Mihalkovics?, can be followed into the 
pars peduncularis (crura) of the mesencephalon. In the Derotremata, 
Amphiuma and Menopoma, this commissure contains few fibres. In 
these animals I first observed a powerful commissure, which I may 
speak of as the superior commissure, passing across the roof of 
2 Zeitschr. f. wiss. Zoologie 20. Bd. p. 308. 
3 Entwicklung des Gehirns p. 73. 
