Nictitating membrane

Nictitating Membrane

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Nictitating membrane

The nictitating membrane (from Latin nictare, to blink) is a transparent or translucent third eyelid

Eyelid

An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body....
present in some animals that can be drawn across the eye

Eye

Eyes are Organ that detect light, and send signals along the optic nerve to the visual system and other areas of the brain. Complex optical systems with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system....
for protection and to moisten the eye while also keeping visibility. Various reptiles, birds, and shark

Shark

Sharks are a type of fish with a full Cartilage skeleton and a highly Streamlines, streaklines and pathlinesd body. They respire with the use of five to seven gill slits....
s have a full nictitating membrane, whereas, in many mammals, there is a small vestigial remnant of the membrane present in the corner of the eye.

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Encyclopedia

The nictitating membrane (from Latin nictare, to blink) is a transparent or translucent third eyelid

Eyelid

Eye

Shark

Polar Bear

The polar bear is a bear native to the Arctic Ocean and its surrounding seas. The world's largest carnivore found on land, and shares the title of largest land predator with the Kodiak Bear, an adult male weighs around , while an adult female is about half that size....
s, seal

Pinniped

Pinnipeds or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine mammals comprising the families Odobenidae , Otariidae , and Phocidae ....
s, and aardvark

Aardvark

The Aardvark is a medium-sized, burrowing, nocturnal mammal native to Africa. It is sometimes called "antbear", "anteater", "Cape anteater" , "earth hog" or "earth pig"....
s, also have a full nictitating membrane. It is often called a third eyelid or haw and may be referred to as the plica semilunaris or palpebra tertia in scientific terminology.

Nictitating membranes are found in bird

Bird

Birds are wing, Bipedalismal, endothermic , vertebrate animals that lay egg . There are around 10,000 living species, making them the most numerous tetrapod vertebrates....
s, reptile

Reptile

Reptiles, or members of the class Reptilia, are air-breathing, cold-blooded vertebrates that have skin covered in scale as opposed to hair or feathers....
s, amphibian

Amphibian

Amphibians , such as frogs, toads, salamanders, newts and caecilians, are cold-blooded animals that metamorphose from a juvenile, water-breathing form to an adult, air-breathing form....
s, fish

Fish

A fish is any marine biology vertebrate animal that is typically ectothermic , covered with scale , and equipped with two sets of paired fins and several unpaired fins....
, but are less common in mammal

Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
s, mainly being present in monotreme

Monotreme

Monotremes are mammals that lay eggs instead of giving birth to live young like Marsupialias and Placentalia .They are conventionally treated as comprising a single order Monotremata, though a recent classification proposes to divide them into the orders Platypoda and Tachyglossa ....
s and marsupial

Marsupial

Marsupials are an infraclass of mammals, characterized by a distinctive Pouch , in which females carry their young through early infancy....
s. In humans, the plica semilunaris and its associated muscles are thought to be the vestigial remnants of the nictitating membrane and its muscles. Charles Darwin reported that the plica semilunaris is slightly larger in Africans and Australian Aborigines than in other peoples. Only one species of primate

Primate

A primate is a member of the biological order Primates , the group that contains lemurs, the Aye-aye, Lorisidaes, galagos, tarsiers, monkeys, and apes, with the last category including humans....
—the Calabar angwantibo

Calabar Angwantibo

The Calabar Angwantibo , also known as the Calabar Potto, is a strepsirrhine primate from the Lorisidae family. It shares the genus Arctocebus with the Golden Angwantibo ....
—is known to have a functioning nictitating membrane.

Unlike human

Human

A human being, also human or man, is a member of a species of bipedalism primates in the family Hominidae . Mitochondrial DNA evidence indicates that modern humans originated in east Africa about 200,000 years ago....
eyelid

Eyelid

An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body....
s, the nictitating membrane moves horizontally across the eyeball. It is normally translucent. In some diving animals, for example beaver

Beaver

Beavers are two primarily nocturnal, semi-aquatic species of rodent, one native to North America and one to Eurasia. They are known for building dams, canals, and lodges ....
s and manatee

Manatee

Manatees are large, fully aquatic marine mammals sometimes known as sea cows. The name manat? comes from the Ta?no, a pre-Columbian people of the Caribbean, meaning "breast"....
s, it moves across the eye to protect it while under water, and in these species it is transparent; in other diving animals including sea lion

Sea Lion

For other uses of the term "sea lion", see Sea lion .Sea lions are any of seven species in six genera of modern pinnipeds including one extinct ....
s, it is activated on land, to remove sand and other debris. This is its function in most animals. In birds of prey, it also serves to protect the parents' eyes from their chicks while they are feeding them. In polar bear

Polar Bear

Snow blindness

Snow blindness is a painful eye condition, caused by exposure of unprotected eyes to the ultraviolet rays in bright sunlight Reflection from snow or ice or less commonly from sea or sand....
. In shark

Shark

Sharks are a type of fish with a full Cartilage skeleton and a highly Streamlines, streaklines and pathlinesd body. They respire with the use of five to seven gill slits....
s it protects the eye while the shark strikes at its prey. Woodpeckers tighten their nictitating membrane a millisecond prior to their beak impacting the trunk of a tree in order to prevent their eyes from leaving their sockets.

In cat

Cat

The cat , also known as the Domestication cat or house cat to distinguish it from other Felinae and Felidae, is a small predationy carnivore species of crepuscular mammal that is valued by humans for its companionship and its ability to hunt vermin, snakes, scorpions, and other unwanted household pests....
s and dog

Dog

The dog is a domesticated subspecies of the Gray Wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties....
s, the nictitating membrane is not usually visible, and its being chronically visible should be taken as a sign of poor condition or ill health. It can, however, be seen clearly when gently opening the eye of the healthy animal when it is asleep, or pushing down/applying pressure on the eyeball will cause it to appear. In some breeds of dogs, the nictitating membrane can be prone to prolapse

Prolapse

Prolapse literally means "To fall out of place." In medicine, prolapse is a condition where organs, such as the uterus, fall down or slip out of place....
, resulting in a condition called cherry eye

Cherry eye

Cherry eye is the term used to refer to canine nictitans gland prolapse, a common eye condition in various dog breeds where the gland of the third eyelid known as the nictitating membrane prolapses and becomes visible....
.

In many species, any stimulus to the eyeball (such as a puff of air) will result in reflex nictitating membrane response. This reflex is widely used as the basis for experiments on classical conditioning

Classical conditioning

Classical Conditioning is a form of associative learning that was first demonstrated by Ivan Pavlov . The typical procedure for inducing classical conditioning involves presentations of a neutral stimulus along with a stimulus of some significance....
in rabbit

Rabbit

Rabbits are small mammals in the family Leporidae of the order Lagomorpha, found in several parts of the world. There are seven different genus in the family taxonomy as rabbits, including the European rabbit , Cottontail rabbit , and the Amami rabbit ....
s.

Nictitating membrane

See also