nictitating membrane


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nictitating membrane

(in reptiles, birds, and some mammals) a thin fold of skin beneath the eyelid that can be drawn across the eye

Nictitating Membrane

 

a third eyelid, located in the inner corner of the eye in some Euselachiae (fishes) and the majority of terrestrial vertebrates. The nictitating membrane is formed from a fold of the conjunctiva and is located behind the upper and lower eyelids. In terrestrial vertebrates, a transparent nictitating membrane periodically covers the cornea to clean and moisten it. Nictitating membranes are most highly developed in reptiles and birds. Among mammals, a third eyelid is absent in Echidna and Cetacea; apes and humans have rudimentary nictitating membranes in the form of semilunar folds.

nictitating membrane

[′nik·ə‚tād·iŋ ′mem‚brān]
(vertebrate zoology)
A membrane of the inner angle of the eye or below the eyelid in many vertebrates, and capable of extending over the eyeball.
References in periodicals archive ?
Every effort was made to directly contact the cornea to obtain measurements, and this proved time consuming because of the constant "flashing" of the nictitating membrane in all birds and with both devices.
50]/g) was found in liver, intestine, brain, adrenal glands, and nictitating membranes of individual cats.
In the slaughter process, upon first strike of the chisel the alligators responded by closing tightly the nictitating membranes and eyelids, tensing of the muscles of the jaws, tensing of the muscles of the neck, and rapid withdrawal of forelimbs; a brief general struggle (although not violent) occurred over a period of approximately two to three seconds.
Their eyes are protected by a nictitating membrane that moves up and down like an eyelid.
O'Rourke discovered that prions collect in pockets of lymphoid tissue in a sheep's nictitating membrane, or third eyelid.
7) Only 2 glands constitute the avian lacrimal apparatus: the gland of the nictitating membrane (formerly Harders gland) and the lacrimal gland.