through reflex action, from the excitement of the retina, so that their
eyes might be protected from the bright light. But they tried their
utmost to look upwards; and now a curious struggle, with spasmodic
twitchings, could be observed between the whole or only the central
portion of the frontal muscle, and the several muscles which serve to
lower the eyebrows and close the eyelids. The involuntary contraction
of the pyramidal caused the basal part of their noses to be
transversely and deeply wrinkled. In one of the three children, the
whole eyebrows were momentarily raised and lowered by the alternate
contraction of the whole frontal muscle and of the muscles surrounding
the eyes, so that the whole breadth of the forehead was alternately
wrinkled and smoothed. In the other two children the forehead became
wrinkled in the middle part alone, rectangular furrows being thus
produced; and the eyebrows were rendered oblique, with their inner
extremities puckered and swollen, in the one child in a slight degree,
in the other in a strongly marked manner. This difference in the
obliquity of the eyebrows apparently depended on a difference in their
general mobility, and in the strength of the pyramidal muscles. In both
these cases the eyebrows and forehead were acted on under the influence
of a strong light, in precisely the same manner, in every
characteristic detail, as under the influence of grief or anxiety.
Duchenne states that the pyramidal muscle of the nose is less under the
control of the will than are the other muscles round the eyes. He
remarks that the young man who could so well act on his grief-muscles,
as well as on most of his other facial muscles, could not contract the
pyramidals.[705] This power, however, no doubt differs in different
persons. The pyramidal muscle serves to draw down the skin of the
forehead between the eyebrows, together with their inner extremities.
The central fasciae of the frontal are the antagonists of the
pyramidal; and if the action of the latter is to be specially checked,
these central fasciae must be contracted. So that with persons having
powerful pyramidal muscles, if there is under the influence of a bright
light an unconscious desire to prevent the lowering of the eyebrows,
the central fasciae of the frontal muscle must be brought into play;
and their contraction, if sufficiently strong to overmaster the
pyramidals, together with the contraction of the corrugator and
orbicular muscles, will act in the manner just described on the
eyebrows and forehead.
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