296 
MR. J. L. CLARKE OK THE INTIMATE STRUCTURE OF THE BRAIN. 
and partially blended with it, is a large and nearly cylindrical column of nerve-cells (Q") 
constituting the principal nucleus of the facial nerve. The cells are much larger than 
those of the superjacent layer, but differ from each other considerably both in shape and 
size, and have a great resemblance to the cells of the hypoglossal nucleus. Their average 
size is smaller in Man than in the higher Mammalia, as the Sheep or Ox. From the 
lateral part of this nucleus bundles of curved fibres (ft") proceed outward in the direction 
of the facial nerve. From the middle of the nucleus other bundles of fibres (S") extend 
forward to the motor nucleus of the trigeminal or fifth cerebral nerve ; and on the inner 
side of the nucleus is another system of fibres (T" T'"), extending, like the former, from 
behind forward, but differing among themselves with regard to their destination. Only 
a part of these transverse fibres, as we shall presently see, issue from the superficial grey 
layer (g 1 ") ; most of them radiate from a longitudinal column, rvhich runs immediately 
beneath it, and which is composed of fibres of the facial and abducens nerves, but chiefly 
of the former. Some of them curve outward and enter the facial nucleus (Q") ; while 
the rest extend forward, in company with those at S" proceeding from the middle of the 
salme nucleus, to reach the motor nucleus of the fifth nerve, and the superior olivary 
body*. 
(47) Another set of transverse fibres (U", U'") crossing at right angles the three sets of 
fibres just described, connect the column of cells (Q"), on the one hand with the audi- 
tory nucleus (at U"), and on the other hand with the opposite side of the medulla across 
the median raphe at V". 
(48) In transverse sections made a little higher up, we see the oval cut-end of a lon- 
gitudinal column, from which the third set of transverse fibres (T"), just described, 
radiate forward. This column is represented at T", fig. 51, Plate XIII. It first makes 
its appearance, however, below the level at which the nerve enters the nucleus, in sec- 
tions intermediate between fig. 50 and fig. 51. In fig. 51 may be observed a number 
of fibres converging from different parts of the superficial grey layer at g'", and turning 
round the oval column (T") to decussate across the raphe, in company with others pro- 
ceeding from the principal nucleus (Q"). Some of these converging fibres, however, 
instead of winding inward round the column to the raphe, run forward as roots of the 
abducens nerve (V'). 
(49) In the Mammalia the facial nuclei differ in some respects from those of Man. 
In the Pabbit the commissural fibres are remarkably well seen. Fig. 48, Plate XII., as 
before stated, represents a transverse section of the left half of the medulla. A little 
below the entrance of the facial nerve, near the median furrow, is the cut-end of the lon- 
gitudinal column (T"), which is more cylindrical than in Man. On the outer side of this 
is the principal nucleus of the facial nerve, included within the crescentic and dotted 
line. The cells of this nucleus are very numerous, but smaller than those of Man, and 
somewhat different in shape. On its outer side are some much larger multipolar cells, 
sparingly scattered, but passing uninterruptedly into the denser group constituting the 
* In the Orang Outang these fibres are uncommonly numerous. 
