When young infants cry they open their mouths widely,
and this, no doubt, is necessary for pouring forth a full volume of sound;
but the mouth then assumes, from a quite distinct cause, an almost
quadrangular shape, depending, as will hereafter be explained, on the firm
closing of the eyelids, and consequent drawing up of the upper lip.
How far this square shape of the mouth modifies the wailing or crying sound,
I am not prepared to say; but we know from the researches of Helmholtz
and others that the form of the cavity of the mouth and lips determines
the nature and pitch of the vowel sounds which are produced.
[7] `Theorie Physiologique de la Musique,' Paris, 1868, P. 146.
Helmholtz has also fully discussed in this profound work the relation
of the form of the cavity of the mouth to the production of vowel-sounds.
It will also be shown in a future chapter that, under the feeling
of contempt or disgust, there is a tendency, from intelligible causes,
to blow out of the mouth or nostrils, and this produces sounds
like pooh or pish. When any one is startled or suddenly astonished,
there is an instantaneous tendency, likewise from an intelligible cause,
namely, to be ready for prolonged exertion, to open the mouth widely,
so as to draw a deep and rapid inspiration.
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