Inprimates, and specifically in humans, thelabia majora (sg.:labium majus), also known as theouter lips orouter labia, are two prominentlongitudinalskin folds that extend downward and backward from themons pubis to theperineum.[1] Together with thelabia minora, they form thelabia of thevulva.
The labia majora arehomologous to the malescrotum.[2]
Labia majora is theLatin plural for big ("major") lips. The Latin termlabium/labia is used in anatomy for a number of usually paired parallel structures, but in English, it is mostly applied to two pairs of parts of thevulva—labia majora andlabia minora. Traditionally, to avoid confusion with other lip-like structures of the body, the vulvar labia were termed by anatomists in Latin aslabia majora (orminora) pudendi.
Embryologically, they develop fromlabioscrotal folds.[3]
The labia majora after puberty may become of a darker color than the skin outside them and growpubic hair on their external surface.
The main function of the labia majora is to cover and protect the other parts of the vulva.[4] The labia majora contain thelabia minora,interlabial sulci,clitoral hood,clitoral glans,frenulum clitoridis, theHart's Line, and thevulval vestibule, where the external openings of theurethra and thevagina are located. Each labium majus has two surfaces, an outer, pigmented and covered with strong,pubic hair; and an inner, smooth and beset with largesebaceous follicles. The labia majora are covered withsquamous epithelium. Between the two, there is a considerable quantity ofareolar tissue andfat, besides vessels,nerves, andglands. Below the skin of the labia majora, there is a tissue called thedartos muliebris, which gives them a wrinkled appearance.[5]
The labia majora constitute the lateral boundaries of thepudendal cleft. The pudendal cleft, also known as thevulvar cleft orcleft of Venus (rima vulvae orrima pudendi in Latin),[6] is a vertical fissure between the labia majora starting at the basal point of themons pubis. After puberty, the clitoral hood and the labia minora can protrude into the pudendal cleft to a variable degree.[7]
The labia majora are thicker in front, and form theanterior labial commissure where they meet below themons pubis. Posteriorly, they are not really joined, but appear to become lost in the neighboring integument, ending close to, and nearly parallel to, each other. Together with the connecting skin between them, they form anothercommissure, theposterior labial commissure, which is also the posterior boundary of the vulva. The interval between the posterior commissure and theanus, from 2.5 to 3 cm in length, constitutes theperineum.[8] The anterior region of the perineum is known as theurogenital triangle, which separates it from the anal region. Between the labia majora and the innerthighs are thelabiocrural folds. Between the labia majora and labia minora are the interlabial sulci. Labia majoraatrophy aftermenopause.
While the labia majora is present in all female primates, many have them until adulthood or become inconspicuous around that period.[9] Primates besides humans that always have visible labia majora arebonobos,strepsirrhines,tarsiers,cebid monkeys, andgibbons.[10][11][12]
In non-primate femalemammals, the labia majora are absent since the labioscrotal swellings have disappeared as a fetus.[13] Because of this, the pudendal cleft refers to the slit between thelabia vulvae in those mammals.[14]
Thefat pad of the labia majora can be used as agraft, often as a so-called "Martius labial fat pad graft", and can be used, for example, inurethrolysis.[15]
One or more of the preceding sentences incorporates text in thepublic domain frompage 1265 of the 20th edition ofGray's Anatomy (1918)
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