74. OSBORN. [Vov. I. 
structure. My observations relate principally to the former. 
The latter has recently been thoroughly investigated by Wlas- 
sak, in a memoir which I have not had an aidan: of study- 
ing, and independently by Koppen. 
In an earlier paper upon the Cerebellum of Gurbiohwenae I 
showed that it receives two lateral systems of fibres on each 
side, one from the medulla, one from the mesencephalon. Also 
a central system entering the mesencephalon. The latter, 
which I mistakenly compared (84, p. 266, Plate VI., Fig. 7) 
with the superior peduncles of the mammalian cerebellum, I now 
find is composed of the cerebellar branch of the descending 
Trigeminus tract. The cerebellum of Asphiuma consists 
exclusively of these lateral and central tracts, containing no 
cells except the lining of ependyma (83, Plate VIIL, Fig. 3). 
The Cryptobranchus cerebellum contains, in addition, a small 
mass of round cells of the same description as those composing 
the central gray substance of the optic lobes. It thus consists 
of the following elements, as shown 1 in Figs. 19, 23 and 28. 
1. Fine fibres from the’ c oe lateral portions 
of the medulla. It is clear that these fibres, cé/.¢', as shown 
in Fig. 18, do not arise from the central region of the medulla. 
They ean in part be followed to the point of exit of the 7th and 
8th pairs of nerves. Of these the larger portion seem tc come 
from the 8th pair. 
2°. Coarse fibres from the descending trigeminus 
tract. The course of these fibres has already been described 
on page 153, 5 7. 
3. Fine fibres passing laterally into the mesen- 
cephalon, co/.t; these can be followed some distance into the 
lateral area of the central gray of the mesencephalon. 
4. A nucleus of small rounded cells, cb/.n, in the 
ventral area. 
The passage of the fibres from the 8th pair through the cere- 
bellum has also been observed by Ahlborn. It is somewhat diffi- 
cult to determine positively, owing to the close similarity between 
the adjoining trigeminal and facial fine fibre bundles. In hori- 
zontal sections the fine fibres of the Trigeminus, 5 2°, are, how- 
ever, seen to pass directly forward into the lateral region of the 
.mesencephalon. It is thus probable that the fibres entering 
from the medulla are mostly sensory fibres from the Auditory 
