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Nictitating membrane

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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 for protection and to moisten it while maintaining vision. [1]

35 relations: Aardvark, Amphibian, Anatomical terms of location, Beaver, Bird, Camel, Canthus, Cherry eye, Classical conditioning, Crocodilia, Eye, Eyelid, Fish, Harderian gland, Homology (biology), Human vestigiality, Lemur, Lorisoidea, Mammal, Manatee, Peregrine falcon, Photokeratitis, Pinniped, Plica semilunaris of conjunctiva, Polar bear, Primate, Prolapse, Reptile, Sea lion, Shark, Tears, Transparency and translucency, Ultraviolet, Vestigiality, Woodpecker.


The aardvark (Orycteropus afer) is a medium-sized, burrowing, nocturnal mammal native to Africa.

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Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia.

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Anatomical terms of location

Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans.

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The beaver (genus Castor) is a large, primarily nocturnal, semiaquatic rodent.

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Birds, also known as Aves, are a group of endothermic vertebrates, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skeleton.

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A camel is an even-toed ungulate in the genus Camelus that bears distinctive fatty deposits known as "humps" on its back.

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Canthus (pl. canthi, palpebral commissures) is either corner of the eye where the upper and lower eyelids meet.

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Cherry eye

Cherry eye is a disorder of the nictitating membrane (NM), also called the third eyelid, present in the eyes of dogs and cats.

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Classical conditioning

Classical conditioning (also known as Pavlovian or respondent conditioning) refers to a learning procedure in which a biologically potent stimulus (e.g. food) is paired with a previously neutral stimulus (e.g. a bell).

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Crocodilia (or Crocodylia) is an order of mostly large, predatory, semiaquatic archosaurian reptiles, known as crocodilians.

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Eyes are organs of the visual system.

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An eyelid is a thin fold of skin that covers and protects the human eye.

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Fish are gill-bearing aquatic craniate animals that lack limbs with digits.

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Harderian gland

The Harderian gland is a gland found within the eye's orbit that occurs in tetrapods (reptiles, amphibians, birds and mammals) that possess a nictitating membrane.

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Homology (biology)

In biology, homology is the existence of shared ancestry between a pair of structures, or genes, in different taxa.

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Human vestigiality

In the context of human evolution, human vestigiality involves those traits (such as organs or behaviors) occurring in humans that have lost all or most of their original function through evolution.

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Lemurs are a clade of strepsirrhine primates endemic to the island of Madagascar.

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Lorisoidea is a superfamily of nocturnal primates found throughout Africa and Asia.

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Mammals are the vertebrates within the class Mammalia (from Latin mamma "breast"), a clade of endothermic amniotes distinguished from reptiles (including birds) by the possession of a neocortex (a region of the brain), hair, three middle ear bones, and mammary glands.

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Manatees (family Trichechidae, genus Trichechus) are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living species in the order Sirenia: the Amazonian manatee (Trichechus inunguis), the West Indian manatee (Trichechus manatus), and the West African manatee (Trichechus senegalensis).

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Peregrine falcon

The peregrine falcon (Falco peregrinus), also known as the peregrine, and historically as the duck hawk in North America, is a widespread bird of prey (raptor) in the family Falconidae.

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Photokeratitis or ultraviolet keratitis is a painful eye condition caused by exposure of insufficiently protected eyes to the ultraviolet (UV) rays from either natural (e.g. intense sunlight) or artificial (e.g. the electric arc during welding) sources.

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Pinnipeds, commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semiaquatic marine mammals.

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Plica semilunaris of conjunctiva

The plica semilunaris is a small fold of bulbar conjunctiva on the medial canthus of the eye.

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Polar bear

The polar bear (Ursus maritimus) is a hypercarnivorous bear whose native range lies largely within the Arctic Circle, encompassing the Arctic Ocean, its surrounding seas and surrounding land masses.

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A primate is a mammal of the order Primates (Latin: "prime, first rank").

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In medicine, prolapse is a condition where organs fall down or slip out of place.

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Reptiles are tetrapod animals in the class Reptilia, comprising today's turtles, crocodilians, snakes, amphisbaenians, lizards, tuatara, and their extinct relatives.

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Sea lion

Sea lions are sea mammals characterized by external ear flaps, long foreflippers, the ability to walk on all fours, short, thick hair, and a big chest and belly.

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Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head.

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Tearing, lacrimation, or lachrymation is the secretion of tears, which often serves to clean and lubricate the eyes in response to an irritation of the eyes.

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Transparency and translucency

In the field of optics, transparency (also called pellucidity or diaphaneity) is the physical property of allowing light to pass through the material without being scattered.

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Ultraviolet (UV) is electromagnetic radiation with a wavelength from 10 nm to 400 nm, shorter than that of visible light but longer than X-rays.

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Vestigiality is the retention during the process of evolution of genetically determined structures or attributes that have lost some or all of their ancestral function in a given species.

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Woodpeckers are part of the family Picidae, a group of near-passerine birds that also consist of piculets, wrynecks, and sapsuckers.

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[1] https://en.wikipedia.org/wiki/Nictitating_membrane

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