681 
the 3rd ventricle just in front of the pineal stalk. Its fibres pass di- 
rectly downwards into the thalami. This seems to correspond to the 
commissure of the pineal stalk which has been observed in the Elasmo- 
branchs, also in mammals, although it is absent in birds. Although 
much reduced in size, it is present both in the Frog and Menobranchus 
and leaves little doubt as to the disputed position of the pineal stalk. 
3) The cerebellum is an extremely degenerate structure in these 
Urodela. In Amphiuma it contains no nerve cells whatever and in dia- 
meter it barely equals the valve of Vieussens of the frogs brain. This 
primitive condition (Menopoma, Amphiuma) enables us to determine 
with precision its relations to other parts. a. From its lower surface 
a set of fibres passes directly forwards into the roof of the optic lobes. 
5. It receives a band of fibres from the extreme lateral poitions of the 
medulla oblongata, while anteriorly, c. a band enters it from the pars 
peduncularis of each side. These two sets would appear to correspond 
to the anterior and posterior peduncles of the mammalian brain and 
the cerebellum itself seems to be wholly composed of the fibres of these 
peduncles. 
4) I have not as yet traced any fibres from the optic lobes to the 
optic nerve, but the course of the fibres in the thalami (Menopoma) 
has been followed with interesting results. Each optic nerve is com- 
posed of fibres springing, a. from the opposite thalamus and, 5. from 
the thalamus of the same side. The former a. arise from the upper 
cell areas of the thalami, sweep around the main longitudinal fibre 
system, (see fibre courses above) and pass through the chiasma to enter 
the nerve of the opposite side: The latter (4) spring from the lower 
cell areas of the thalami and pass directly into the optic nerve of the 
same side; they are quite distinct from those of the inferior com- 
missure of Gudden which is here well developed. This shows that, 
as regards the fibres springing from the thalami, the amphibian and 
higher mammalian brains are closely similar, and that the decussation 
is not complete as is generally affirmed 5. 
5) My series of sections strongly confirm Goette’s® statement 
that in the adult Amphibian brain the pineal process is quite invisible 
to the naked eye and that most anatomists are wholly mistaken as to 
the nature and position of this body. The little reddish body lying 
between the hemispheres, which is usually described and figured as the 
pineal body is in fact a continuation of the plexus chorioideus 
medius which in the Amphibia has been thrust upwards in a remark- 
4 Mihalkovics, Entwicklung des Gehirns p. 103. 
5 Wiedersheim, Vergleichende Anatomie 1882. p. 334. 
6 Entwicklung der Unke p. 315. 
