5. What is the function of the
iris and of the pupil?

Gap-fill exercise

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The iris works like diaphragm of a
photographic since it has
muscles contractor relax varying
the diameter. When the luminous
heightens the parasympathetic
nervous commands the
contraction of pupil; when there is
of light the sympathetic
system stimulates the dilation
the pupils. These movements
upon the muscles of iris.