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which time these birds remain hidden in dark holes; or if indeed
they are compelled to come out into the open air lighted up by the
sun, they contract their pupils so much that their power of sight
diminishes together with the quantity of light admitted.
Study the anatomy of various eyes and see which are the muscles
which open and close the said pupils of the eyes of animals.
[Footnote: Compare No. 24, lines 8 and fol.]
8
30.
a b n is the membrane which closes the eye from below, upwards,
with an opaque film, c n b encloses the eye in front and behind
with a transparent membrane.
It closes from below, upwards, because it [the eye] comes downwards.
When the eye of a bird closes with its two lids, the first to close
is the nictitating membrane which closes from the lacrymal duct over
to the outer corner of the eye; and the outer lid closes from below
upwards, and these two intersecting motions begin first from the
lacrymatory duct, because we have already seen that in front and
below birds are protected and use only the upper portion of the eye
from fear of birds of prey which come down from above and behind;
and they uncover first the membrane from the outer corner, because
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