273
FIFTH PAIR OF NERVES.
the same part as the greater packet, and poste¬
rior to it. (See Jig. 140). This view of the con¬
nection of the lesser packet, if confirmed, must
lead to interesting results with regard to the rela¬
tions of the two portions of the fifth nerve at least ;
it will at all events decide the question as yet in
dispute, whether they are to be regarded as
distinct nerves, or parts of the same ; upon
this point further light will be thrown by the
disposition of the same part in fish, in which
the source of the uncertainty prevailing with
regard to the nerve in the higher classes does
not exist to the same amount ; inasmuch as the
ganglionic and non-ganglionic divisions of the
nerve seem for the greater part associated in
their distribution.
Fig. 141.
Back view of pons, bulb, and course of the Fifth
Nerve in man.
18 Tubercula quadrigemina.
19 Continuation upward of the tract from which
the Fifth Nerve arises.
The other references indicate the same parts as
in the preceding figure.
When the adjoining matter has been care¬
fully cleared away from the part to which the
packets of the nerve are attached, that part ap¬
pears to be a longitudinal tract of a yellowish-
white colour, composed of fibres running in the
same direction, and capable of being followed
both upward and downward : upward this tract
seems continued beneath the superior peduncle
of the cerebellum ;* downward it descends from
* Of the nature of the structure continued up¬
ward from the attachment of the nerve the author
is not satisfied : it presents, when cleared, the ap¬
pearance given to it in fig. 141,19, but it is very cine-
ritious in character, and he is not prepared to say
whether it be a continuation of the tract from which
the nerve appears to arise, or a part of the floor of
the fourth ventricle at its upper extremity, con¬
nected to the attachment of the nerve : the mode
in which the nerve arisès in the bird and the turtle
appears to the author opposed to the opinion that
the tract to which the nerve is attached is, in them
at least, any thing more than a continuation or
VOL. 1L.
behind the pons into the spinal bulb, and after
a short course divides into two cords, one for
each column of the spinal marrow (see Jigs.
140, 141). At the entrance of the tract into
the bulb it is situate deep, before the floor of
the fourth ventricle and behind the superficial
attachment of the two portions of the seventh
pair, which must be separated from each other
and displaced in order that it may be ex-*
posed : externally the tract corresponds to the
peduncles of the cerebellum, and is united in¬
ternally to the cineritious matter of the floor
of the ventricle. At the point of attachment
the tract presents a somewhat prominent en¬
largement, (figs. 140, 141, 12,) which the au¬
thor will venture to call an eminence, though
with hesitation, lest it be considered an ex¬
aggeration, from which the nerve may be held
to arise.
It is said that the nerve may be held to arise
from this tract, because, though it be certainly
not its ultimate connection with the brain, and
though cords can be traced from it to more
remote parts, yet the union of the cords at the
point, and the attachment of both portions of
the nerve to it, seem to mark it as the origin
of the nerve ; the change of character too which
will be described as occurring at the attach¬
ment of the nerve, countenances the opinion
that the tract is not simply a continuation of
the nerve.
It may be doubted whether the eminence
really exist, or whether it be not merely the
result of dissection : the author will not insist
upon it, but several considerations induce him
to consider it real : in the first place, he almost
uniformly finds it,* and secondly, it seems to
be a common point to the two portions of the
nerve and to the other cords, which form part
of its encephalic connections ; and lastly, this
view is corroborated by the disposition of the
same part in other animals ; for a similar ap¬
pearance will be found, at the attachment of
the nerve behind the pons, in other mammalia
as well as in man after the separation of the
adjoining matter, e. g. in the horse ; and it is
even asserted by Desmoulins that an eminence
may be observed naturally upon the floor of
the fourth ventricle, in some animals, at the
attachment of the nerve. His statement is :
“ on observe même dans les rongeurs, les
taupes, et les hérissons, un petit mamelon ou
tubercle sur l’extremité antérieure du bord du
ventricule ; mamelon, dans lequel se continuent
les fibres postérieures de la cinquième paire, et
de l’acoustique.’7 When the tract has reached
the point at which the inferior peduncle of the
cerebellum first inclines outward toward the
hemisphere, it separates, as has been stated, into
two parts or cords, (seefigs. 140, 141,) destined,
one, as is already known, to the posterior, the
other, according to the author’s belief, to the an¬
terior column of the spinal cord. The course and
disposition of these cords are remarkable and
root of the nerve, but admitting this, he cannot*
satisfy himself that it is to be regarded in the same
light in the Mammalia.
* The attachment of both the packets must be
made out, el^e the enlargement -will not appear.
T