60 OSBORN. EVormit: 
II. The optic nerves are, as a rule, very much reduced in the 
Urodela, and are in a degenerate condition in the Pvotezda. 
Both in the Proteus and Necturus the primitive epiblastic 
stalk of the optic vesicles is persisent. In Proteus 
and in some examples of Vecturus the lumen of the stalk is 
persistent in the adult condition.! This lumen opens into the 
i-like expansion of the bottom of the 3d ventricle, which is 
almost invariably found just in front of the chiasma, and demon- 
strates that this recessus opticus is the proximal portion 
of the primitive optic stalk. 
III., IV., VI. These nerves require no special comment. 
Their development is naturally parallel with that of the 2d pair. 
I have made a doubtful observation of the presence of the 
3d pair in Proteus, but have seen no trace of the 4th and 6th, 
although it is quite possible that their rudiments will be found 
in sections. The 3d and 4th pairs pass off independently. 
The 6th pair, according to Fischer (64, p. 125), unites with 
the Trigeminus. I have not been able to determine whether 
this passes into or through the Gasserian ganglion or unites 
with the 5th beyond it. The more difficult problems arise with. 
regard to the homologies of the Trigeminal, Facial, and Acous- 
tic nerves, which can only be settled by obtaining serial sections 
through the nerves, brain, and skull zz sztw. This arises from 
the fact that the Trigeminus is always reinforced by a branch of 
the Facial, and that the latter and Acoustic are given off so 
close together that it is difficult to determine into what bundle 
the minor roots of each pass. A clear idea of the exit of these 
nerves, as found in Cryptobranchus, is given in Fig. 6, which is 
reconstructed from the sections, while the relation of the nerves 
to the encephalic tracts is given in Fig. 21; see also Figs. 15 
to 18. 
V., VII. The main division of the Trigeminus is given off as 
a single root from the antero-lateral region of the medulla, V. 1, 
2, and it is reinforced by two smaller roots, V. 3.2. The Facial 
1 This fact when observed was communicated to Professor Kupffer, who made use 
of it in a paper upon the relation of the growth of the optic nerve to the stalk. The 
epithelial stalk in long sections extends outwards from the recessus opticus as far as 
the nerve can be followed, and is peripheral, the fibres lying at the side. 
2 Fischer described four branches from the Gasserian ganglion, instead of the usual 
three, in Siredon (op. cit., p. 128): 1. To the skin of the nose region; this he be- 
