ME. J. L. CLAEKE ON THE INTIMATE STEUCTUEE OE THE BE AIN. 
297 
outer auditory nucleus (d o), to which they seem to belong. The superficial grey layer 
forming the floor of the fourth ventricle is deeper than in Man, and contains larger and 
more numerous cells. Fig. 52, Plate XIII. represents the same parts in the Babbit 
more highly magnified. The longitudinal column (T") is closely encircled by a dense 
layer of fibres, which, after reaching its inner side, run for the most part together across 
the raphe to decussate with their fellows immediately below the median furrow (h"). 
In this course they are joined by other fibres proceeding from the column itself. . Some 
of them, however, instead of crossing the raphe appear to become longitudinal at the 
point (A'"). Adjoining this layer of fibres, on the left or outer side of T", and forming 
the chief part of the same commissural system, is a broad fan-shaped expansion of fibres, 
which converge inward to the front of the longitudinal column (T"), where they inter- 
lace each other in an intricate plexus (7d 7(7), between a multitude of longitudinal bundles 
(represented by the dark masses) with intervening multipolar cells. The greater number 
make their way through this plexus to the raphe to decussate with their fellows of the 
opposite side ; while the rest, instead of running to the raphe, bend forward precisely 
in the direction of the abducens nerve (7c"), and joining in the general plexus between 
longitudinal bundles and nerve-cells advance towards the front of the medulla. It is 
probable, however, that many of these transverse fibres communicate their influence 
longitudinally by means of their connexion with the numerous nerve-cells, of which some 
of the processes run with the longitudinal bundles and form part of their constituent 
fibres; for such an arrangement I have discovered in other portions of the medulla 
having the same general appearance. If such be the case, the interlacement of the 
transverse fibres, and their communication with different longitudinal bundles, provide 
for a wonderfully extensive and complicated commissural connexion between parts at 
different levels. On considering the parts from which this fan-shaped system of trans- 
verse fibres is derived, we find that some of them issue from different portions of the 
superficial grey layer (g" g"') with different degrees of curvature forward and inward ; 
that others come from the neighbourhood of the auditory nucleus (d o) ; and that many 
arise out of the large group of cells included in the crescentic dotted line, and consti- 
tuting the principal nucleus of the facial nerve*. All the fibres derived from both g" 
and d o, d o, run into this nucleus ; but whether they all pass through it to reach the 
plexus or the raphe I cannot decide. It is probable that some of them, at least, are 
commissural between the facial nucleus and the parts from which they are derived, 
Of the Facial Nerve. 
(50) It was evident to me that the complicated course and connexions of the facial 
nerve could never be accurately ascertained by the method hitherto adopted of examining 
transverse sections alone. The plan pursued by myself was as follows. Having first 
ascertained the exact course and connexions of the nerve, as exhibited in transverse 
sections, I then carefully made a succession of longitudinal sections in planes inclining 
* The cells have been omitted in order to show more plainly the fibres which pass through it. 
2 T 2 
