THE FIFTH NERVE.
591
which the latter nerve arises, has not been the seat of an undisco¬
vered lesion.
The lingual branch of the fifth is likewise a nerve of touch, t>r
common sensation; the tongue derives its sense of touch from this
nerve and from the glosso-pharyngeal. The division of the lingual
branch of the fifth nerve has been observed both by Magendie, Des¬
moulins, and myself to be very painful. It is possible that there are.
special filaments for taste and touch associated in it. The chorda
tympani, at all events, may be looked upon as destined for common
sensibility.
The nervous fibres endowed with the sense of taste may be super-
added to very different nerves. In birds the nerve of taste is a branch
of the glosso-pharyngeal, in frogs it is a branch of the vagus.
M. Magendie (Journ. de Physiol. iv. 302,) asserts that he has
seen nearly all the senses annulled by the division of the trunk of
the fifth nerve within the cranium. The loss of vision he inferred
from the animal not noticing the light of a lamp. But rabbits are
frequently not affected by light, even when the fifth nerve is not
divided: and M. Magendie himself confesses that, when the light of
the sun was allowed to break in where lights had been previously
excluded, the eyelids of the animal closed; and this was seen still
more distinctly when the light was thrown into the eye through a
lens. M. Magendie demonstrates by experiment on animals what
is known too well from the observation of diseases in man, namely,
that when the optic nerve is paralysed, its function—the perception
of light—is not performed by the fifth; but he is of opinion that the
fifth is at least an auxiliary to the optic nerve, and necessary for the
due performance of the visual function. M. Magendie believes also
that the fifth is necessary for hearing.
The circumstance of an animal not being susceptible of other im¬
pressions immediately after the division of so large a nerve as the
fifth, proves nothing more than that it has suffered a serious injury.
We know, in fact, that the division of large nerves,—for instance, of
the optic nerve,—gives rise to serious symptoms. According to my
view, the fifth nerve has no influence either on vision, hearing, or
smell. In an epileptic patient, in whom there was inflammation of
the eye and opacity of the cornea on the right side, with loss of
vision, and subsequently insensibility of the eyelids, nose, and tongue
on the same side, deafness of the right ear, and a scorbutic state of
the gums, M. Ser/es found the portio major of the fifth nerve in a
diseased state as far back as the pons Varolii, (Magendie'’s Journ.
v. 232;) but here blindness was the consequence of the opacity of the
cornea. All the other affections of the senses, as well as the convul¬
sions of the right side of the body, are accounted for by the diseased
state of the brain. The inferences which have been drawn from this
case are moreover shown to be completely groundless by another
case of disease of the whole trunk of the fifth, in which there was
insensibility of the entire left side of the head, of the nose, tongue,
and eye, while vision remained perfect. (Muller’s Archiv. für
Anal, und Physiol. 1834, p. 132.)