Structure: 

The hymen is a thin, ring-shaped fold of mucus membrane that partially or fully covers the vaginal orifice. [1] During the perinatal period, the hymen naturally wears down and opens, with only remnants of the hymen (hymenal caruncles) remaining visible. These remnants serve as the border between the vagina and the vestibule of the vagina. [1] 

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Function:

 The hymen is considered an embryological remnant and does not have an established physiological function. [1] During embryonic development, the uterovaginal primordium, which is formed through the earlier fusion of the paramesonephric ducts, projects into the dorsal wall of the urogenital sinus. [1] This induces the formation of the sinovaginal bulbs which are paired endodermal tissue outgrowths that extend dorsally from the urogenital sinus. [1] The sinovaginal bulbs fuse to form the solid vaginal plate, which then canalizes and develops into the inferior 2/3 of the vagina. [1] The canal of the vagina that is formed is separated from the urogenital sinus cavity by the membranous hymen. [1] During the perinatal period, the membranous hymen perforates and remains as a thin fold of membrane within the vaginal orifice. [2]

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The state of the hymen is frequently used as evidence in cases of child abuse and rape. [1] There is a common misconception that virginity is associated with the state of the hymen and that, upon vaginal intercourse for the first time, the hymen breaks and bleeds. [3] This misconception persists despite scientific evidence showing that the hymen is not a reliable marker for previous sexual activity. [3]

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In 1 of 1000 newborn girls, the hymen can fail to open during the perinatal period, resulting in an imperforate hymen that obstructs the vaginal opening. [4] In most cases, this only becomes an issue upon menstruation where the menstrual blood accumulates since it cannot pass through the vaginal opening. [4] This can result in cyclic abdominal pain, perceived absence of menstruation, and obstruction of the urinary tract. [4]