76 OSBORN. [VoL. II. 
cephalon, while the secondary or more local tracts of the enceph- 
alon can in most cases be followed directly to certain nuclei. 
The latter are more numerous in the Azwra than in the Uvodela, 
at least they are much more sharply defined. The following 
nuclei have been observed in the brains of both classes (see 
Fig. 31). 
A. The nuclei of) tiie, cranialymerves: 
1°.. The nuclei of the 3d, 4th, and 6th pairs, 37, 47, and 6m, 
are nearly upon the same horizontal level in the Uvrodela. 
2°. The great mesencephalic trigeminal nucleus extends along 
either side of the entire roof of the segment in many of the 
Urodela, but in the Aura is much smaller and is mainly con- 
fined to the antero-lateral region (Fig. 26). 
3°. Two special well-defined centres of the optic nerve fibres 
are observed: a. the roof of the mesencephalon on either side 
of the median line in the Uvodela; in the Anuva this extends 
into the widely expanding optic lobes. 9. A distinct nucleus in 
the middle region of the walls of the diencephalon (corpus 
geniculatum). 
B. The nuclei of the encephalic tracts 
1°. The most distinct of these are the ganglia habenarum, 
gh, just anterior to and partly traversed by the superior com- 
missure. They are composed of small, rounded cells, like those 
of the central gray at the dorsal anterior angle of the thalami. 
2°. In the floor of the mesencephalon, just posterior to the 
oculo-motor nucleus, is the ganglion interpedunculare, 
gi, composed of very small triangular cells. 
3°. Just posterior to the posterior commissure is a small dor- 
sal nucleus, in the course of the optic tract (see Fig. 24), the 
connections of which are undetermined. 
4. The corpus striatum is not well defined in the Am- 
phibia ; it consists of a mass of scattered cells, slightly anterior 
and ventral to the anterior commissure, Fig. 28, cs. 
5°. Slightly posterior to the oculo-motor nucleus, on the same 
horizontal level, is a nucleus of pale bipolar ganglion cells quite 
distinct in character from the nucleus of the third pair, which 
consists of triangular deeply stained cells. This is figured, but 
not lettered, in Fig. 23, and is seen both in Rana and C7ypio- 
branchus (? red nucleus). 
6°. The most conspicuous nucleus in Rava is the nucleus 
