304 ME. J. L. CLARKE ON THE INTIMATE STRUCTURE OF THE BRAIN. 
tribute to form these bundles proceed, not from the nucleus (Q"), but, as already shown, 
in the case of the lower roots (fig. 51) from different parts of the superficial grey layer 
of the fasciculus teres ( g " </'"), and in their way outward cross the decussating fibres of 
the facial nerve, just where these are about to enter the longitudinal column (T"). 
(62) It is evident, then, that both the abducens and the facial nerves arise each 
from two separate nuclei, as well as from the same nuclei. In longitudinal sections 
of the pons Yarolii, both in Man and animals, I have repeatedly endeavoured to ascer- 
tain whether any of the fibres of the abducens nerve turn round and run longitudi- 
nally upward, but I have never been able to perceive the slightest indication of such a 
course. Indeed, as already stated, the roots curve slightly downward on reaching the 
fasciculus teres , although I have never succeeded in tracing them any further in that 
direction *. 
(63) Having ascertained the relations and connexions of the facial and abducens 
nuclei and of the longitudinal column (T") in transverse sections, and in oblique-longitu- 
dinal sections along the plane in which this column is entered by the facial nerve, I 
wished, further, to ascertain their relations to parts situated both above and below them 
in the medulla. For this purpose I first made a succession of longitudinal but hori- 
zontal sections from side to side along the surface of the fourth ventricle, beginning at 
the level of the facial nerve and nuclei (along the horizontal dotted line in fig. 51, 
Plate XIII.), and carrying the section downward through the hypoglossal nucleus to 
about the horizontal dotted line in fig. 32, Plate XI. Such a section of the left half of 
the medulla and of a small portion of the right half is represented in fig. 57, Plate XIV. 
Here we find that a large number of fibres belonging to the lower end of the longitudinal 
column (T"), instead of curving forward to the antero - lateral part of the pons (s", figs. 53, 
54, & g'", fig. 55, Plate XIII.), spread laterally and curve horizontally outward just below 
the surface of the ventricle. Some of these fibres pass through the facial nucleus (Q"), 
but the greater number sweep round its lower end across the base of the grey tubercle 
(e' e') at its junction with the inner auditory nucleus, i (compare fig. 51, Plate XIII.). 
In this course they are met by another set of horizontal fibres radiating inwards from 
the outer auditory nucleus or column (c'o, fig. 57). In fig. 51, Plate XIII. the fibres 
* Stilling, who was the first to trace the facial and abducens nerves to the fasciculus teres, considers that 
both these nerves arise from the common nucleus (Q"). He did not, however, trace any of their roots beyond 
this point. Scheobee van bee Kolk denies that they arise from a common nucleus, and in forming this opi- 
nion he seems to have been influenced, as on many other occasions, by physiological views, rather than by 
actual observation. His objections on the ground that the two nerves have very different functions, are of no 
value in the face of positive observation. It is certainly difficult to understand why the two nerves, which are 
apparently never associated in action (except perhaps in certain cases of facial expression), should arise from 
the same nuclei ; but even if the abducens could not be traced to the nuclei of the facial, it is equally difficult 
to understand why its fibres are so closely interlaced with those of the facial, while it is separated by the whole 
length of the pons Yarolii from the third nerve with which it is so closely associated in action. Scheobee van 
bee Kolk says that all the roots of the abducens terminate in the floor of the fourth ventricle, and that they 
seem to bend upward “ into a nucleus of ganglionic groups placed externally and superiorly to the facial 
nerve. 
