A man contracts these muscles when he violently blows his nose.
I asked one of my boys to shout as loudly as he possibly could,
and as soon as he began, he firmly contracted his orbicular muscles;
I observed this repeatedly, and on asking him why he had every time
so firmly closed his eyes, I found that he was quite unaware of the fact:
he had acted instinctively or unconsciously.
It is not necessary, in order to lead to the contraction of
these muscles, that air should actually be expelled from the chest;
it suffices that the muscles of the chest and abdomen should contract
with great force, whilst by the closure of the glottis no air escapes.
In violent vomiting or retching the diaphragm is made to descend
by the chest being filled with air; it is then held in this position
by the closure of the glottis, "as well as by the contraction of its own
fibres."[13] The abdominal muscles now contract strongly upon the stomach,
its proper muscles likewise contracting, and the contents are thus ejected.
During each effort of vomiting "the head becomes greatly congested,
so that the features are red and swollen, and the large veins of
the face and temples visibly dilated.
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