Don't know what you mean by 'serious.' Do you mean 'serous' as in fluid-filled?
The membrane that can cover over a frog/toad's eyes (and other amphibian, reptile, even mammal species) is known as a 'nictating' membrane. It is there to protect against fluid and debris from coming into contact with the corneal surface of those eyes.
Conjunctiva is the mucous membrane that covers the front of the eye.
The aqueous humor is the mucous membrane that lines the eyelids and covers the front of the eye.
This is the cornea.
Nictitating membrane.
conjunctiva
conjunctiva
Crocodilians have a transparent nictating membrane which serves as a secondary eyelid. This inner eyelid moves from the sides while the outer eyelid moves up and down. When this transparent eye-lid is engaged, it does limit visual ability somewhat, especially in muddy, darker water. However, it protects the main eye from damage that may be caused by debris in the water (or even during scuffles with fellow crocodilians). When visual ability is limited, crocodilians have a keen sense of smell to help back them up.
The nictitating membrane is part of a frog's eye. It is just above the lower lid and acts as a protective third eyelid.
The nictitating membrane is a translucent membrane at the bottom of the eye that can be pulled up right across the eye. It is not an eyelid because the frog can still see when the membrane is raised. It is used when swimming or when insects are swarming around the frog's eyes, and also for keeping the eyes moist when it is windy.
The nictitiating membrane protects the eye so frogs can see in water.
The nictitating membrane (from Latin nictare, to blink) is a transparent or Translucentthird Eyelidpresent in some animals that can be drawn across the Eyefor protection and to moisten the eye while also keeping visibility. Various reptiles, birds, and Sharkhave a full nictitating membrane, whereas, in many Mammals, there is a small Vestigialremnant of the membrane present in the corner of the eye. Some mammals, such as Camel, Polar_bear, Pinniped, and Aardvark, also have a full nictitating membrane. It is often called a third eyelid or haw and may be referred to as the Plica_semilunaris_of_the_conjunctivaor palpebra tertia in scientific terminology.Nictitating membranes are found in Bird, Reptile, Amphibian, Fish, but are less common in Mammal, mainly being present in Monotremeand Marsupial.Answers.comIn humans, the plica semilunaris and its associated muscles are thought to be the vestigial remnants of the nictitating membrane and its muscles.Answers.comCharles Darwin reported that the plica semilunaris is slightly larger in Africans and Australian Aborigines than in other peoples.Answers.comOnly one species of Primate---theCalabar_angwantibo---isknown to have a functioning nictitating membrane.Answers.comFile:Haliaeetus_leucocephalus_LC0198.jpgFile:Haliaeetus_leucocephalus_LC0198.jpgThe nictitating membrane (mid-blink) of a Bald_EagleFile:Gray892.pngFile:Gray892.pngThe plica semilunaris is thought to be the vestigial remnant of a nictitating membrane in humans.Unlike the upper and lower eyelids, the nictitating membrane moves horizontally across the eyeball. It is normally translucent. In some diving animals, for example Beaverand Manatee, 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, 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, and when Peregrine_falconsgo into their 200 mph dives, they will blink repeatedly with the nictitating membrane to clear debris and spread moisture across the eye. In polar bears it protects the eyes from Snow_blindness. In sharks it protects the eye while the shark strikes at its prey. Woodpeckerstighten 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.Answers.comThe nictitating membrane in Catand Dogdoes not have many muscle fibers and consequently 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, resulting in a condition called Cherry_eye. Birds can actively control their nictitating membraneAnswers.comIn 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_conditioningin Rabbit.Answers.comi hope that answers your question =D
cornea
It is called a nictating membrane.
The clear curved membrane that covers the front of the eye is called the cornea. It also focuses light onto the retina.
cornea
myothelial tiisue
The cornea, or clear layer on the front of the eye.
The transparent layer forming the front eye
The nictitating membrane is the transparent layer the covers the outside of a frogs eye. Frogs have a so-called Nictitating membrane, which they can slide over their eyes for protection. They do this while jumping and swimming.
They have a transparent membrane that covers the eye when they submerge.
Cataracts are a clouding of the lens of the eye or of its surrounding transparent membrane that obstructs the passage of light.
The cornea is responsible for focusing the light that enters the eye. It is the transparent portion of the eye that covers the front of the eye
The front clear surface of the eye is called the cornea. It protects the covering of the eye and helps to focus light.