156 JULIA WORTHINGTON. 
equal and symmetrical (fig. 1). Its roof is continuous with 
that of the mid brain, although superficially a shght depres- 
sion marks the boundary between the two sections. ‘lhe two 
lobes are divided in the dorso-median line by a continuation 
of the dorsal cleft that divides the mid brain lobes. The 
cerebellum rests solidly upon the dorsal surface of the forward 
end of the medulla (figs. 1, 6), covering the anterior end of 
the fourth ventricle, and, in consequence, has no peduncles. 
In structure it consists of an outer glia layer, similar to and 
a continuation of the outer glia layer of the mid brain, and 
an inner mass of cells. In the base of the cerebellum, on 
each side of the median line, lying partly in the cerebellum, 
and partly in the mid brain, is a group of from ten to fifteen 
multipolar giant-cells. Most of these cells send their axones 
back into the medulla, though whether all do or not lam not 
yet prepared to say. ‘These cells are apparently like the 
Mauthner cells of the medulla. Lying close under the dorsal 
surface of the cerebellum is a decussation of fibres connecting 
its two lobes, a continuation backward of the dorsal decussa- 
tion of the mid brain. 
The cerebellum has also two other very prominent sets of 
fibres. Coming up from the floor of the tween brain, running 
dorso-caudad in the lateral walls of the cerebellum to end 
among the cells of its roof, are the fibres of the great tractus 
olfacto-cerebellaris, described above. Mesial to these, 
lying between them and the giant cells, are the fibres of 
another tract, equally important, the tractus cerebello- 
spinalis. ‘These fibres, arising in the roof of the cerebellum, 
run ventro-caudad, and gather into two strong bundles, one 
on each side, at the caudal end of the cerebellum, just lateral 
to the groups of giant cells. On leaving the cerebellum, 
these bundles turn sharply latero-caudad. When the brain 
is dissected out, and its fore part is deflected downward, 
away from the medulla, as in fig. 4, these tracts are seen for 
a little distance in relief upon the dorsal surface of the 
medulla (fig. 4, tv. c.s.). Not for long, however, for they 
quickly plunge beneath the surface, penetrating between the 
