ME. J. L. CLAEKE ON THE INTIMATE STEITCTUEE OE THE BEAIN. 
299 
of fig. 55. It must be understood that in fig. 55 the nucleus Q!' beneath the loop extends 
under the trunk of the nerve q" ; and that in fig. 56 T" is the loop cut transversely. More- 
over, these two sets or strata of fibres decussate each other at the first bend of the loop ; 
for some from the deep or anterior stratum (q", fig. 56) run first transversely and 
obliquely backward from W", and then longitudinally downward , along the posterior 
portion of the loop at U ; while others from the superficial or posterior stratum (l') run 
first transversely but obliquely forward from W'", and then longitudinally downward 
along the anterior and middle portion of the loop at T", U', which represents a transverse 
section of it in the direction of the line Q!", fig. 55. It is evident, then, that the descend- 
ing fibres of the loop cannot be parallel, but must intersect each at different angles, as 
shown in fig. 55, Plate XIII., which represents exactly the appearances presented by a 
very thin slice of the loop made in the plane of its course, and magnified about 100 dia- 
meters. Some of the fibres of the superficial stratum are seen to extend backward to 
the superficial grey layer (g'", fig. 56); while many of those belonging to the deep 
stratum (q") curve forward into the group of cells (Q"). But the proper fibres of the 
nerve are evidently joined and crossed by others which proceed from the smaller group 
of cells (v”, fig. 55), and from the superjacent grey layer of the ventricle. 
(51) The lower arm of the loop (q"', fig. 55) is smaller, looser, or less sharply defined 
than the trunk of the nerve (q"), and hangs gracefully forward like a plume of feathers. 
Many of its fibres droop into the facial nucleus (Q") over which the loop is formed, and 
which is traversed moreover by a large number of longitudinal bundles communicating 
with each other in the manner of a plexus. 
(52) We shall now see what important light is thrown by this dissection on the other- 
wise inexplicable appearances presented in transverse sections. If we make a transverse 
section inclining somewhat upward through the medulla, in the direction of the line 
W" W", fig 55, Plate XIII., and therefore in a plane passing through the lower arm of 
the loop ( q ■"), we have the appearances presented in fig. 50, Plate XIII., which, however, 
is more highly magnified. In this figure we see that the set of transverse fibres (T”, T"'), 
of which the origin was exceedingly obscure, belong to the lower arm of the loop (q m , 
fig. 55), and that their apparent abruptness of origin is due to the circumstance of their 
having been cut across at the point where they change their course from longitudinal to 
transverse. If we make another transverse section a little higher up, between the arms 
of the loop, in the direction Q", Q w , fig. 55, it is evident that instead of seeing the set of 
fibres (T", fig. 50) which emanate abruptly from beneath the superficial grey layer (g"'), 
we shall see the transversely-cut surface of the longitudinal portion of the loop. In 
Man this cut surface is almost perfectly oval (T", fig. 51, Plate XIII.), but in the Rabbit 
(fig. 52) and some other animals it is more circular. The positions of the cut-ends of its 
fibres evidently show that these fibres are not parallel ; and this appearance is quite 
explained by the decussation along the summit of the loop, at Q'". 
(53) If a transverse section be now made along the lower side of the trunk of the 
nerve ( q ", fig. 55, Plate XIII.), in the direction of the line g'", g'"', we find that its fibres, 
