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The nictitating membrane of a masked lapwing as it closes over the left eye, originating from the medial canthus. The nictitating membrane (from Latin nictare, to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision.
All geckos except those in the subfamily Eublepharinae (eyelid geckos) possess brilles. Some groups of bony fish have a transparent eyelid known as the adipose eyelid . [ 3 ] Some reptiles, mammals and birds have a translucent third eyelid that moves horizontally across the eye called the nictitating membrane .
An epicanthic fold or epicanthus [6] is a skin fold of the upper eyelid that covers the inner corner (medial canthus) of the eye. [3] However, variation occurs in the nature of this feature and the presence of "partial epicanthic folds" or "slight epicanthic folds" is noted in the relevant literature.
Glass lizards have eyelids and can blink, but snakes have immovable, transparent scales and can’t blink. Snakes can unhinge their jaws to swallow large prey, but glass lizards can’t.
Cephalopods, as active marine predators, possess sensory organs specialized for use in aquatic conditions. [1] They have a camera-type eye which consists of an iris, a circular lens, vitreous cavity (eye gel), pigment cells, and photoreceptor cells that translate light from the light-sensitive retina into nerve signals which travel along the optic nerve to the brain. [2]
Since they cannot blink, species without eyelids generally lick their own brilles when they need to clear them of dust and dirt, in order to keep them clean and moist. [3] Unlike most lizards, geckos are usually nocturnal [4] and have excellent night vision; their colour vision in low light is 350 times more sensitive than human eyes. [5]
Like snakes and most geckos, they have no eyelids, but unlike snakes, they have external ear holes and flat, unforked tongues. [3] They are native to Australia and New Guinea. [4] Pygopodids have no fore limbs at all, but they do possess vestigial hind limbs in the form of small, flattened flaps. [3]
These lizards are often distinguishable from snakes on the basis of one or more of the following characteristics: possessing eyelids, possessing external ear openings, lack of broad belly scales, notched rather than forked tongue, having two more-or-less-equal lungs, and/or having a very long tail (while snakes have a long body and short tail). [1]