to the angle of the mouth and the upper lip. Hence the lateral
drawing of the lips, the elevation of the upper lip disclosing the
teeth, the very peculiar elevation of the nostrils without their being
expanded (for we breathe only through the mouth in laughing);
hence too the dimple in the cheek, where the acting muscles congregate;
and hence the fulness of the cheek, rising so as to conceal
the eye and throw wrinkles about the lower eyelids and the
temples, whilst the skin of the chin is drawn tight by the retraction
of the cheeks and the opening of the jaws. Thus it is
obvious that the whole moveable features are raised upwards. The
orbicular muscles of the eyelids do not partake of the relaxation of
the mouth; they are excited so as to contract the eyelids and sink
the eye, whilst the struggle of a voluntary effort of the muscles to
open the eyelids and raise the eyebrow gives a twinkle to the eye
and a peculiar obliquity to the eyebrow, the outer part of it being
most elevated.
I have stated that it is the nerve I call respiratory which produces
all this extended influence upon the features, and that with
the loss of the power of that nerve there is a total extinction of
this expression. We have a confirmation of this in witnessing the
further influence of the passion in agitating the whole extent of
the respiratory nerves and muscles. He holds his sides to control
the contractions of the muscles of the ribs. The diaphragm is
violently shaken. The same influence spreads to the throat, and
the sound of laughter is as distinct and peculiar as the signs in
the face.
Defining laughter according to the anatomy, it is a certain influence
of the respiratory nerve of the face, which produces relaxation
of the orbicular muscle of the lip, whilst it excites the class
of ringentes, and the orbicular muscles of the eyelids into action.
In what then does it differ from its opposite, the expression of pain
or crying ?
CRYING.