The eyelids are made of layers of muscle and cartilage with an outer
surface of skin and an inner surface which is a continuation of the
conjunctiva that covers the eyeball. In the edge of the eyelid a series
of tiny glands are embedded. The mouths of these open on the margin of
the lids. The eye-lashes, whose duty it is to act as a screen,
preventing foreign bodies such as dust or other air-born objects getting
into the eye, are also inserted in the edge of the lid.