( 901 ) 
Lophius). The exact course of both these roots was, however, never 
clear before. 
As I had at my disposal some frontal and horizontal series of 
Gadus and other fishes, | was able to trace the whole system with 
fairly great exactness and arrived at the following conclusion. 
In Lophius piscatorius the decussation of the trochlear root-fibres 
takes place in a fairly simple way. After their origin in the trochlear 
nucleus, the fibres pass in the form of one compact bundle closely 
round the aquaeduct upwards, and cross im foto on one and the 
same vertical level, the decussation occupying about 6 sections of 
25 a, but not more; a difference can only be observed between the 
fibres mutually in so far as some decussate closer to the aquaeduct, 
others closer to the surface of the velum, a few even after the exit 
(somewhat as in Scheme 0 fig. 4). 
In Hippoglossus this relation is rather 
more complicated, owing to some of the 
fibres following a pathway separated from 
the others. Before proceeding to decussation, 
these fibres (about half of the total number) pass 
frontally into the valvula cerebelli; then only 
do they decussate and after the decussation 
they turn laterally, run again caudally be- 
tween the valvula cerebelli and its connec- 
tion with the tectum, to appear at the height 
of the original velum out of the groove 
between mesencephalon and _ cerebellum 
simultaneously with the other root-bundle 
which has decussated on the original level 
(somewhat as in Scheme c, fig. 4). 
The impression is conveyed as if the 
anterior part of the trochlear-root and its 
decussation were drawn frontally by the growth of the valvula into 
the optic ventricle under fixation of tbe point of exit. 
This dislocation is the most conspicuous in the case of the anterior 
roct-half in Gadus, where the valvula protrudes somewhat farther 
forward under the tectum (ef. Scheme d fig. 12). 
Besides by the peculiar dispersion of decussations, the anterior 
part of the IV root of this animal is also distinguished from the 
posterior by the fact that it does not run directly round the aquaeduet 
medially from the tr. cerebello-mesencephalicus, but runs outside that 
tract (Fig. 11) as has also been observed by Kappers (l.c. p. 62). 
That the frontal shifting of a part of the decussation is caused by 
