136 J. B. JOHNSTON, 
1) Bundle y, from the ventro-lateral columns in the region of 
the commissura ansulata (Phot. 18, cf. page 99). This is a con- 
spicuous bundle of very heavily medullated coarse fibres which is 
seen in frontal sections spreading out in fan-shape in the base of 
the mid brain. Some of the fibres pierce the fasciculus longitudinalis 
posterior and others run farther laterad. All seem to come from 
the ventro-laterai tracts, among which they bend caudad (sagittal 
sections). Going forward and upward the fibres collect into a dense 
bundle close to the cavity of the mid brain, which runs dorsally 
forming the cephalic part of the bridge to the cerebellum. The 
bundles enter the dorsal part of the valvula and end as above de- 
scribed. This bundle is not shown in Pl. 13. 
2) Nervus trochlearis. — The fourth nerve is very small, 
containing in all probably less than fifty fibres. The cells of its 
nucleus are not impregnated in my preparations. The fibres form 
a small distinct bundle which can be recognized in frontal sections 
at about the level of the fasciculus. The bundle runs dorsally near 
the cavity and just caudal to bundle y, becomes completely imbedded 
in that bundle as it passes into the valvula, turns caudad and leaves 
bundle y, decussates in the velum and emerges between the cere- 
bellum and mid brain in the usual manner. 
3) Tractus lobo-cerebellaris rectus, first bundle. A 
small bundle from the fine-fibred portion of this tract. Compare 
page 134). 
4) Tractus tegmento-cerebellaris. — The neurites of 
cells in the nucleus ruber tegmenti run in the fine-fibred portion 
of the direct tractus lobo-cerebellaris. They probably enter the 
medulla with the bundle last mentioned. Or, it is possible that (3) 
is made up of fibres from the nucleus ruber and that all the fine 
fibres of the direct tractus lobo-cerebellaris reach the medulla. 
Which is true can only be determined by the method of degeneration. 
5) Tractus lobo-cerebellaris cruciatus, first bundle. 
Compare page 134. 
6) Tractus lobo-cerebellaris cruciatus, second bundle. 
Runs immediately over the cephalic surface of the secondary vagus 
nucleus (page 134). 
7) Tractus lobo-cerebellaris rectus, second bundle. 
Contains the greater part of the coarse fibres of the direct tract 
(cf. page 134). 
