So that this muscle seems to aid in the erection of the hairs on the head
of man. in the same manner as the homologous _panniculus carnosus_ aids,
or takes the greater part, in the erection of the spines on the backs
of some of the lower animals.
_Contraction of the platysma myoides muscle_.--This muscle is spread
over the sides of the neck, extending downwards to a little beneath
the collar-bones, and upwards to the lower part of the cheeks.
A portion, called the risorius, is represented in the woodcut
(M) fig. 2. The contraction of this muscle draws the corners of
the mouth and the lower parts of the checks downwards and backwards.
It produces at the same time divergent, longitudinal, prominent ridges
on the sides of the neck in the young; and, in old thin persons,
fine transverse wrinkles. This muscle is sometimes said not to be
under the control of the will; but almost every one, if told to draw
the corners of his mouth backwards and downwards with great force,
brings it into action. I have, however, heard of a man who can
voluntarily act on it only on one side of his neck.
Sir C. Bell[21] and others have stated that this muscle is strongly
contracted under the influence of fear; and Duchenne insists so strongly
on its importance in the expression of this emotion, that he calls it
the _muscle of fright_.
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