tory nerves in particular, perform ? They combine in the act of
speaking without doubt, and I shall make it equally manifest that
they are also the organs of expression.
In the first place, comparative anatomy, that is, the comparison
of these nerves in different animals, exhibits profusion and seeming
intricacy, in proportion to the animal’s powers of expression. Every
one must have observed, not merely the resemblance in the face of
the monkey to the features of man, but also that activity and
grimace, which bear the same proportion to the expression of the
human countenance. The nerves of the face and neck of the
monkey are numerous, and have frequent connexions. But on
cutting the respiratory nerve of the face of the monkey, the features
become dead to the influence of the creature’s passions. Yet after
such an experiment the skin is sensible, and the muscles of the
jaws and tongue are capable of the actions of chewing and swallowing,
only there is no grimace or expression to be seen. If the
respiratory nerve of one side be cut, the expression of that side is
utterly extinguished, while the chattering and mewing, the scowl
of the eyebrow, and the grinning of the lips and cheek, remain on
the other side.
There is a great deal of expression in a dog, whether we attend
to the wistful and friendly look with which he regards his master’s
face, or when he is placed in fierce opposition to another dog.
All the fire of expression disappears the instant that the nerve of
respiration is divided. He will fight as bitterly, but with no
retraction of his lips, or sparkling of his eye, or drawing back of
his ears. The face is inanimate, it does not partake of the action
corresponding with the passion, though the muscles of the face and
jaws, as far as they are liable to influence through other nerves,
continue their offices.
By cutting the same nerve in a cat it may be deprived of all
expression. If the nerve of one side of the head be cut, as it comes
out before the ear, we shall see no brilliancy in the eye from the
action of the eyelids, no motion of the whiskers, nor spitting in
anger; although all these signs be exhibited on the opposite side.
If birds be deficient in expression, from the horny bill being
substituted for the mouth and nostrils, yet they are not without
some sign of passion in the rising and flutter of the feathers. The
game cock, in the position of fighting, spreads a ruff of feathers
round his head. The position of his head, and the feathers raised
from his neck, are the expressions of hostile excitement. But on
the division of the respiratory nerve the feathers are no longer
raised, although the disposition to spar continues.
The accidental injury or the disease of the respiratory nerve of
the face of man exhibits the same consequences with these experiments
on brutes. When the respiratory nerve is injured on one
side, the individual can neither laugh nor weep with that side of