Eyelid

Role

The eyelids play several parts with respect to the eyes:

to protect the eyes of certain aggressions like projections from poussières ;
to block or limit the Light penetrating in the eye (for example at the time of the Sleep) ;
to contribute with the rehydration and the cleaning of the Cornea.

Structure

The eyelids are actuated by Muscle S which allow the opening and closing. They belong to the protective additional bodies. At the man, the eyelids are two mobile musculo-membranous veils which recover and protect the former part of the sphere from the eye. They are consisted seven superimposed layers:

a fine skin: thin and mobel
a cellular layer of fabric releases
orbicular muscle of the eyelids
second cellular layer of fabric releases
a layer fibro elastic
a layer of smooth muscle fibers
a mucous layer

On the free edges of the eyelid are established the lashes on three or four rows. Close to the interior angle is the lacrimaux points and the caruncle (which contains sébacées and lachrymal glands). At the Mammifère S the eyelids are two, in top and bottom, and the eyelid top is more mobile.
The Cil S - small hairs on the edge of the eyelids - help with protection by blocking dust before they do not reach the Cornée.

At the Reptile S the eyelids are in general with the number of three. Two are in top and bottom, that of bottom being more mobile, and a third, side and under the preceding ones, is sometimes semi-transparent.

It should be noted that in certain reptiles like the Snake S or the majority of the geckos it do not have there eyelids but a transparent scale which protects the eye.

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