[17] With respect to the internal vessels,
Dr. Gunning has lately recorded a case of exophthalmos in
consequence of whooping-cough, which in his opinion depended
on the rupture of the deeper vessels; and another analogous
case has been recorded. But a mere sense of discomfort would
probably suffice to lead to the associated habit of protecting
the eyeball by the contraction of the surrounding muscles.
Even the expectation or chance of injury would probably
be sufficient, in the same manner as an object moving too
near the eye induces involuntary winking of the eyelids.
We may, therefore, safely conclude from Sir C. Bell's observations,
and more especially from the more careful investigations
by Professor Donders, that the firm closure of the eyelids
during the screaming of children is an action full of meaning
and of real service.
We have already seen that the contraction of the orbicular muscles
leads to the drawing up of the upper lip, and consequently,
if the mouth is kept widely open, to the drawing down of
the corners by the contraction of the depressor muscles.
The formation of the naso-labial fold on the cheeks likewise
follows from the drawing up of the upper lip.
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