None of the foregoing cases appear to throw any light on
the contraction of the platysma from fear; but it is different,
I think, with the following cases. The gentleman before referred to,
who can voluntarily act on this muscle only on one side of his neck,
is positive that it contracts on both sides whenever he is startled.
Evidence has already been given showing that this muscle
sometimes contracts, perhaps for the sake of opening the mouth widely,
when the breathing is rendered difficult by disease, and during
the deep inspirations of crying-fits before an operation.
Now, whenever a person starts at any sudden sight or sound,
he instantaneously draws a deep breath; and thus the contraction
of the platysma may possibly have become associated with the sense
of fear. But there is, I believe, a more efficient relation.
The first sensation of fear, or the imagination of something dreadful,
commonly excites a shudder. I have caught myself giving
a little involuntary shudder at a painful thought, and I
distinctly perceived that my platysma contracted; so it does if I
simulate a shudder. I have asked others to act in this manner;
and in some the muscle contracted, but not in others.
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