vagina(redirected from external vagina of the optic nerve)
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vagina:see reproductive systemreproductive system,
in animals, the anatomical organs concerned with production of offspring. In humans and other mammals the female reproductive system produces the female reproductive cells (the eggs, or ova) and contains an organ in which development of the fetus takes
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(1) A sheath of various animal and plant organs—for ex-ample, the vagina of a tendon, of a nerve fiber, and of the notochord in certain fishes (Holocephali, Dipnoi, and Acipenseridae). The vagina of a leaf is the lower part of a leaf widened in the form of a canal and slightly (in the Umbelliferae) or greatly (in the grasses) extended to embrace the stem. The vagina protects the bud contained in the axil. In grasses, the vagina is a delicate extension of the base of the internode of the stem. In bananas, the vaginae of the leaves overlap one another to form a false high stem. In many plants the lower leaves, and in some plants all the leaves, are reduced and consist of a single vagina. Vagina is also the name given to the small saclike sheath or edging at the base of the stem of certain hymenomycetous fungi (fly agaric and death cup); it is the vestige of the so-called general spathe that surrounds the fruiting body of a young fungus and later ruptures. The presence (or absence) and the shape of both types of vagina is a regular characteristic used in classifying plants.
(2) The invagination of the skin in animals that serves as a receptacle of some organs is also called a vagina—for example, the vagina of a feather, of a hair, and of the tongue in snakes.
(3) The terminus of the genital canal in female mammals (marsupial and placental) that is used in sexual intercourse and for the emergence of the fetus. In some invertebrates (in several flatworms), the vagina is in the form of a tubelike twisting of the skin with one end opening to the outside and the other end facing the parenchyma. In tsetse flies, larvae develop in the dilated vagina. In mammals the vagina developed from the lower portion of the oviduct. It is paired in marsupials; in placental animals the oviducts merge to form a single vagina. The vagina changes further down into a shortened urogenital sinus which in female mammals forms the vestibule of the vagina. In marsupials, ungulates, rodents, lemurs, and primates, the hymen is situated between the vagina and the vestibule of the vagina.
(4) A muscular, distensible tube situated in the lesser pelvis of a woman between the urinary bladder and urethra in front and the rectum in back. In an adult, the vagina is approximately 7-8 cm in length along the anterior wall and 1.5-2 cm longer along the posterior wall. The direction of the vagina corresponds to the slope of the pelvis and forms a 100-110° angle with the corpus uteri. Entry into the vagina in virgins is blocked by the hymen. The vaginal wall consists of epithelial, muscular, and connective-tissue layers. It is lined with a mucous membrane that forms transverse folds and longitudinal ridges that diminish with age. These folds make it possible for the vagina to stretch considerably (for example, during birth as the fetus passes through). The vagina contains a small quantity (about 1 ml) of fluid, which is formed from blood serum seeping from the vascular walls and glandular discharges in the canal of the cervix uteri. The presence of lactic acid in this fluid makes it bactericidal. The vagina is the terminus of the genital conduction paths.
V. V. KUPRIANOV