88 J. B. JOHNSTON, 
neurites in various directions, but they can not be traced far enough 
to show what is their destination. It is only in the ventral part of 
the nucleus that I have found neurites which could be traced beyond 
the limits of the nucleus itself. These run mesad or ventro-mesad 
among the coarse medullated fibres of the tractus lobo-bulbaris 
cruciatus (Phot. 16 and PI. 12), and are lost before the ventral 
raphe is reached. Whether these fibres end in motor nuclei in the 
medulla or pass forward to the lobi inferiores or elsewhere is a 
matter of speculation. It is possible that they cross to the opposite 
side and have the same destination as those which cross in the 
commissures through the cerebellum. 
In addition to the cells just described there are fusiform cells 
measuring 10—16 by 16—24 u, with two long thick, dendrites. They 
are disposed, for the most part, in the transverse plane and some 
are so placed that one dendrite extends (with the neurites of other 
cells) into the commissure half 
way through the cerebellum. It 
| \ seems probable that the neurites 
valı of these cells go off from the 
f \ ends of the dendrites in the 
| commissures as is the case in 
certain cells in the nucleus taeniae 
in the fore brain (page 142). 
The three commissures of 
the secondary vagus. nuclei lie 
in nearly the same horizontal 
plane in the ventral part of the 
valvula. They are small and are 
sometimes interconnected by 
small bundles. As they pass 
through the cerebellum the fibres 
give off numerous collaterals. In 
Plate 12 I have represented the 
commissures as consisting of 
fibres of the secondary tracts as 
well as neurites from the nucleus. 
I am not sure that any fibres of the secondary tract enter the 
commissures, since I have been unable to trace any such fibres into 
it individually. That fibres arising from the cells of the nucleus 
enter the commissures there can be no doubt. 
Fig. D. 
