The brain of Acipenser. 99 
There enter the cerebellum two other bundles which will be 
more fully described later (page 136). The one bundle (y) comes 
from the base of the mid-brain, its fibres emerging from among 
those of the fasciculus longitudinalis posterior and the antero-lateral 
tracts in the vicinity of the nucleus of the IV nerve. I have been 
unable to find the cells of origin of these fibres. The fibres are 
coarse and varicose and heavily medullated, and are very well im- 
pregnated throughout the greater part of their course. They run 
parallel with the fibres of the IV nerve and enter the valvula at 
the very cephalic border of the bridge connecting with the mid- 
brain. They then pass dorsally on the lateral surface of the valvula 
to its dorso-cephalic surface where they turn mesially and in part 
decussate, in part turn ventrally into the median part of the valvula. 
In this way they are distributed generally to the dorsal and cephalic 
portions of the valvula. The fibres are coarse and very varicose, 
lose their medullation as they enter the valvula and are beautifully 
impregnated, so that they present a striking and characteristic ap- 
pearance in all my preparations. They end for the most part in 
relation with the PURKINJE cells of this region which were described 
above as having moniliform or varicose dendrites. The same cells 
are surrounded to a greater or less extent by fibres of the tracts 
from the tectum and the inferior lobes. The second tract referred 
to consists of fibres from the nucleus ruber tegmenti which run with 
the fine-fibred portion of the direct tractus lobo-cerebellaris et bul- 
baris, and have the same distribution in the cerebellum. 
Apparently all the fibres which leave the cerebellum go by way 
of the cerebellar crest, including two bundles which leave the crest 
at about the cephalic end of the acusticum to go to the base of 
the medulla. One of these runs from the inner surface of the cere- 
bellar crest into the internal part of the acusticum (page 83) and 
the fibres seem to have the same disposition as the internal arcuate 
fibres from the cells of the acusticum. The other leaves the ex- 
ternal surface of the crest in front of the lobus lineae lateralis and 
passes ventrad on the external surface of the medulla (cf. page 190). 
B. The Mid Brain. 
The side walls and base of the mid brain are largely made up 
of tracts of fibres, most of which arise in the grey nuclei of the 
tween brain. Added to these are fibre tracts connecting the tectum 
opticum with the hypothalamus and hind brain, and a large number 
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