Labia majora

In primates, and specifically in humans, the labia majora (sg.: labium majus), also known as the outer lips or outer labia, are two prominent longitudinal skin folds that extend downward and backward from the mons pubis to the perineum.^[1] Together with the labia minora, they form the labia of the vulva.

Labia majora
Labia majora of a human
Details
Precursor	Labioscrotal swellings
Part of	Vulva
Artery	Deep external pudendal artery, superficial external pudendal artery, posterior labial arteries
Vein	Posterior labial veins, internal pudendal veins
Nerve	Perineal branches of posterior femoral cutaneous nerve, genital branch of genitofemoral nerve, posterior labial nerves, anterior labial nerves, pudendal nerve, perineal nerve
Identifiers
Latin	labium majus pudendi
TA98	A09.2.01.003
TA2	3549
FMA	20367
Anatomical terminology [edit on Wikidata]

The labia majora are homologous to the male scrotum.^[2]

Etymology

Labia majora is the Latin plural for big ("major") lips. The Latin term labium/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 the vulva—labia majora and labia minora. Traditionally, to avoid confusion with other lip-like structures of the body, the vulvar labia were termed by anatomists in Latin as labia majora (or minora) pudendi.

Embryology

Embryologically, they develop from labioscrotal folds.^[3]

The labia majora after puberty may become of a darker color than the skin outside them and grow pubic hair on their external surface.

Function and structure

The main function of the labia majora is to cover and protect the other parts of the vulva.^[4] The labia majora contain the labia minora, interlabial sulci, clitoral hood, clitoral glans, frenulum clitoridis, the Hart's Line, and the vulval vestibule, where the external openings of the urethra and the vagina are located. Each labium majus has two surfaces, an outer, pigmented and covered with strong, pubic hair; and an inner, smooth and beset with large sebaceous follicles. The labia majora are covered with squamous epithelium. Between the two, there is a considerable quantity of areolar tissue and fat, besides vessels, nerves, and glands. Below the skin of the labia majora, there is a tissue called the dartos muliebris, which gives them a wrinkled appearance.^[5]

Pudendal cleft

Front view of the vulva. Pudendal cleft at 3.

The labia majora constitute the lateral boundaries of the pudendal cleft. The pudendal cleft, also known as the vulvar cleft or cleft of Venus (rima vulvae or rima pudendi in Latin),^[6] is a vertical fissure between the labia majora starting at the basal point of the mons pubis. After puberty, the clitoral hood and the labia minora can protrude into the pudendal cleft to a variable degree.^[7]

Commissures

A) anterior commissure, B) fourchette, C) posterior commissure

The labia majora are thicker in front, and form the anterior labial commissure where they meet below the mons 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 another commissure, the posterior labial commissure, which is also the posterior boundary of the vulva. The interval between the posterior commissure and the anus, from 2.5 to 3 cm in length, constitutes the perineum.^[8] The anterior region of the perineum is known as the urogenital triangle, which separates it from the anal region. Between the labia majora and the inner thighs are the labiocrural folds. Between the labia majora and labia minora are the interlabial sulci. Labia majora atrophy after menopause.

In non-human primates

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 are bonobos, strepsirrhines, tarsiers, cebid monkeys, and gibbons.^[10][11][12]

In non-primate female mammals, 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 the labia vulvae in those mammals.^[14]

Use in grafting

The fat pad of the labia majora can be used as a graft, often as a so-called "Martius labial fat pad graft", and can be used, for example, in urethrolysis.^[15]

See also

• Anatomy portal
• Femalia
• Labia pride

References

1. Blüm, Volker (2012). Vertebrate Reproduction: A Textbook. Springer Berlin Heidelberg. p. 74. ISBN 978-3-64271-074-2. Retrieved November 19, 2023.
2. "Sex Organ Homologies". www.meddean.luc.edu. Retrieved 2020-08-09.
3. Manual of Obstetrics. (3rd ed.). Elsevier. pp. 1-16. ISBN 9788131225561.
4. Kinsey, Brian (2011). Human Body From A to Z. Marshall Cavendish Reference. p. 465. ISBN 978-0-76149-976-3. Retrieved September 29, 2023.
5. Fahmy, Mohamed A. Baky (2021). Normal and Abnormal Scrotum. Springer International Publishing. p. 69. ISBN 978-3-03083-305-3. Retrieved December 29, 2023.
6. Gould, George M. (1936). Brownslow, C. V (ed.). Gould's Pocket Pronouncing Medical Dictionary (10 ed.). P. Blakinston's Son & C., Inc.
7. Hennekam, RC; Allanson, JE; Biesecker, LG; Carey, JC; Opitz, JM; Vilain, E (June 2013). "Elements of morphology: standard terminology for the external genitalia". American Journal of Medical Genetics. Part A. 161A (6): 1238–63. doi:10.1002/ajmg.a.35934. PMC 4440541. PMID 23650202.
8. One or more of the preceding sentences incorporates text in the public domain from page 1265 of  the 20th edition of Gray's Anatomy (1918)
9. Sheets-Johnstone, Maxine (2010). The Roots of Thinking. Temple University Press. p. 184. ISBN 978-1-43990-365-0. Retrieved November 19, 2023.
10. Ankel-Simons, Friderun (2012). Primate Anatomy: An Introduction. Elsevier Science. p. 523. ISBN 978-0-08046-911-9. Retrieved November 19, 2023.
11. Rosenblum, Leonard A. (2013). Primate Behavior: Developments in Field and Laboratory Research · Volume 2. Elsevier Science. p. 251. ISBN 978-1-48327-182-8. Retrieved November 19, 2023.
12. Poiani, Aldo (2010). Animal Homosexuality: A Biosocial Perspective. Cambridge University Press. p. 156. ISBN 978-1-13949-038-2. Retrieved November 19, 2023.
13. Kumar, M.S.A. (2015). Clinically Oriented Anatomy of the Dog & Cat. Linus Learning. p. 1254. ISBN 978-1-60797-552-6.
14. Studdert, Virginia P.; Gray, Clive C. (2011). Saunders Comprehensive Veterinary Dictionary E-Book. Elselvier Health Sciences. p. 1183. ISBN 978-0-70204-744-2.
15. Carey, J. M.; Chon, J. K.; Leach, G. E. (2003). "Urethrolysis with martius labial fat pad graft for iatrogenic bladder outlet obstruction". Urology. 61 (4): 21–25. doi:10.1016/S0090-4295(03)00117-1. PMID 12657357.

External links

• Labia Majora Medical Definition (Archived 2016-03-04 at the Wayback Machine)