Editing Vagina (section)

==Other animals==

[[File:Cambridge Natural History Mammalia Fig 047.png|thumb|1902 illustration of the female reproductive system of a [[European rabbit]] (vagina labeled "va")]]
The vagina is a structure of animals in which the female is [[internal fertilization|internally fertilized]], rather than by [[traumatic insemination]] used by some invertebrates. Although research on the vagina is especially lacking for different animals, its location, structure and size are documented as varying among species. In [[theria|therian mammals]] ([[Placentalia|placentals]] and [[marsupial]]s), the vagina leads from the uterus to the exterior of the female body. Female placentals have two openings in the vulva; these are the urethral opening for the urinary tract and the vaginal opening for the genital tract. Depending on the species, these openings may be within the internal [[Urogenital sinus#Other animals|urogenital sinus]] or on the external vestibule.<ref>{{cite book|last=Linzey|first=Donald W.|title=Vertebrate Biology: Systematics, Taxonomy, Natural History, and Conservation|publisher=Johns Hopkins University Press|year=2020|page=306|isbn=978-1-42143-733-0|url=https://books.google.com/books?id=Rur4DwAAQBAJ&pg=PA306|access-date=3 December 2024|archive-date=22 January 2024|archive-url=https://web.archive.org/web/20240122190826/https://books.google.com/books?id=Rur4DwAAQBAJ&pg=PA306|url-status=live}}</ref> Female marsupials [[Marsupial#Female reproductive system|have two lateral vaginas]], which lead to separate uteri, but both open externally through the same orifice;<ref>{{Cite book |last=Tyndale-Biscoe |first=C. Hugh |url=https://books.google.com/books?id=KqtlPZJ9y8EC&q=vagina |title=Life of Marsupials |date=2005 |publisher=Csiro Publishing |isbn=978-0-643-06257-3 |language=en}}</ref> a third canal, which is known as the median vagina, and can be transitory or permanent, is used for birth.<ref name="Tyndale-BiscoeRenfree1987">{{cite book|author1=Hugh Tyndale-Biscoe|author2=Marilyn Renfree|title=Reproductive Physiology of Marsupials|url=https://books.google.com/books?id=HpjovN0vXW4C|date=January 30, 1987|publisher=Cambridge University Press|isbn=978-0-521-33792-2|access-date=August 18, 2018|archive-date=February 15, 2017|archive-url=https://web.archive.org/web/20170215191713/https://books.google.com/books?id=HpjovN0vXW4C|url-status=live}}</ref> The female [[spotted hyena]] does not have an external vaginal opening. Instead, the vagina [[Female genitalia of spotted hyenas|exits through the clitoris]], allowing the females to urinate, copulate and give birth through the clitoris.<ref name="courtship">{{cite journal |vauthors=Szykman M, Van Horn RC, Engh AL, Boydston EE, Holekamp KE |year=2007 |title=Courtship and mating in free-living spotted hyenas |url=http://tuvalu.santafe.edu/~bowles/Dominance/Papers/SzykmanetalHyenaMatingBehaviour2007.pdf |journal=Behaviour |volume=144 |issue=7 |pages=815–846 |doi=10.1163/156853907781476418 |bibcode=2007Behav.144..815S |citeseerx=10.1.1.630.5755 |access-date=April 24, 2014 |archive-date=November 30, 2012 |archive-url=https://web.archive.org/web/20121130193631/http://tuvalu.santafe.edu/~bowles/Dominance/Papers/SzykmanetalHyenaMatingBehaviour2007.pdf |url-status=dead }}</ref> In female [[coyote|canids]], the vagina contracts during copulation, forming a [[Canine reproduction#Copulation|copulatory tie]].<ref name = "Bekoff">{{Cite journal |vauthors=Bekoff M, Diamond J |title=Precopulatory and Copulatory Behavior in Coyotes |journal=[[Journal of Mammalogy]] |volume=57 |issue=2 |pages=372–375 |date=May 1976 |jstor=1379696 |doi=10.2307/1379696}}</ref> Female [[Cetacea|cetaceans]] have vaginal folds that are not found in other mammals.<ref>{{Cite book |last1=Perrin |first1=William F. |url=https://books.google.com/books?id=2rkHQpToi9sC&pg=PA427 |title=Encyclopedia of Marine Mammals |last2=Würsig |first2=Bernd |last3=Thewissen |first3=J. G. M. |date=2009-02-26 |publisher=Academic Press |isbn=978-0-08-091993-5 |language=en}}</ref><ref>{{Cite book |last1=Würsig |first1=Bernd |url=https://books.google.com/books?id=mfjYEAAAQBAJ&pg=PA90 |title=Sex in Cetaceans: Morphology, Behavior, and the Evolution of Sexual Strategies |last2=Orbach |first2=Dara N. |date=2023-09-25 |publisher=Springer Nature |isbn=978-3-031-35651-3 |language=en}}</ref>

[[Monotreme]]s, [[bird]]s, [[reptile]]s and [[amphibian]]s have a [[cloaca]] and is the single external opening for the gastrointestinal, urinary, and reproductive tracts. Some of these vertebrates have a part of the [[oviduct]] that leads to the cloaca.<ref name="Iannaccone">{{cite book|vauthors=Iannaccone P|title=Biological Aspects of Disease|publisher=[[CRC Press]]|isbn=978-3-7186-0613-9|year=1997|pages=315–316|url=https://books.google.com/books?id=CNt2tOsBnc8C&pg=PA315|access-date=October 27, 2015|archive-date=May 6, 2016|archive-url=https://web.archive.org/web/20160506182528/https://books.google.com/books?id=CNt2tOsBnc8C&pg=PA315|url-status=live}}</ref><ref name="Fishbeck">{{cite book|vauthors=Fishbeck DW, Sebastiani A|title=Comparative Anatomy: Manual of Vertebrate Dissection|publisher=Morton Publishing Company|isbn=978-1-61731-004-1|year=2012|pages=66–68|url=https://books.google.com/books?id=JijAAgAAQBAJ&pg=PA66|access-date=October 27, 2015|archive-date=April 24, 2016|archive-url=https://web.archive.org/web/20160424114909/https://books.google.com/books?id=JijAAgAAQBAJ&pg=PA66|url-status=live}}</ref> Chickens have a vaginal aperture that opens from the vertical apex of the cloaca. The vagina extends upward from the aperture and becomes the egg gland.<ref name="Fishbeck" /> In some [[jawless fish]], there is neither oviduct nor vagina and instead the egg travels directly through the body cavity (and is fertilised externally as in most [[fish]] and amphibians). In insects and other [[invertebrate]]s, the vagina can be a part of the oviduct (see [[insect reproductive system]]).<ref name="Chapman">{{cite book|vauthors=Chapman RF, Simpson SJ, Douglas AE|title=The Insects: Structure and Function|publisher=[[Cambridge University Press]]|isbn=978-0-521-11389-2|year=2013|pages=314–316|url=https://books.google.com/books?id=NXJEi8fo7CkC&pg=PA314|access-date=October 27, 2015|archive-date=May 6, 2016|archive-url=https://web.archive.org/web/20160506231049/https://books.google.com/books?id=NXJEi8fo7CkC&pg=PA314|url-status=live}}</ref> Birds have a cloaca into which the urinary, reproductive tract (vagina) and gastrointestinal tract empty.<ref>{{Cite news|url=https://www.thespruce.com/glossary-definition-cloaca-385197|title=What Is a Bird's Cloaca?|work=The Spruce|access-date=January 13, 2018|archive-date=January 13, 2018|archive-url=https://web.archive.org/web/20180113203138/https://www.thespruce.com/glossary-definition-cloaca-385197|url-status=live}}</ref> Females of some waterfowl species have developed vaginal structures called dead end sacs and clockwise coils to protect themselves from [[Sexual coercion among animals|sexual coercion]].<ref name="twenty six">Brennan, P. L. R., Clark, C. J. & Prum, R. O. Explosive eversion and functional morphology of the duck penis supports sexual conflict in waterfowl genitalia. Proceedings: Biological Sciences 277, 1309–14 (2010).</ref>

A lack of research on the vagina and other female genitalia, especially for different animals, has stifled knowledge on female sexual anatomy.<ref name="Yong E">{{cite web|vauthors=Yong E|title=Where's All The Animal Vagina Research?|publisher=[[National Geographic Society]]|date=May 6, 2014|access-date=June 6, 2018|url=https://www.nationalgeographic.com/science/phenomena/2014/05/06/wheres-all-the-animal-vagina-research/|archive-date=July 7, 2018|archive-url=https://web.archive.org/web/20180707172541/https://www.nationalgeographic.com/science/phenomena/2014/05/06/wheres-all-the-animal-vagina-research/|url-status=dead}}</ref><ref>{{cite web|vauthors=Cooper D|title=Female genitalia shunned by researchers|publisher=[[ABC Online]]|date=May 7, 2014|access-date=June 6, 2018|url=http://www.abc.net.au/science/articles/2014/05/07/3999220.htm|archive-date=January 11, 2019|archive-url=https://web.archive.org/web/20190111010513/http://www.abc.net.au/science/articles/2014/05/07/3999220.htm|url-status=live}}</ref> One explanation for why male genitalia is studied more includes penises being significantly simpler to analyze than female genital cavities, because male genitals usually protrude and are therefore easier to assess and measure. By contrast, female genitals are more often concealed, and require more dissection, which in turn requires more time.<ref name="Yong E"/> Another explanation is that a main function of the penis is to impregnate, while female genitals may alter shape upon interaction with male organs, especially as to benefit or hinder [[reproductive success]].<ref name="Yong E"/>

Non-human [[primate]]s are optimal models for human biomedical research because humans and non-human primates share physiological characteristics as a result of [[evolution]].<ref name="Sarmento">{{cite book|vauthors=Sarmento B|title=Vitro Culture Models|publisher=[[Woodhead Publishing]]|isbn=978-0-08-100114-1|year=2015|page=296|url=https://books.google.com/books?id=GdmoBAAAQBAJ&pg=PA296|access-date=January 14, 2018|archive-date=July 3, 2019|archive-url=https://web.archive.org/web/20190703221609/https://books.google.com/books?id=GdmoBAAAQBAJ&pg=PA296|url-status=live}}</ref> While menstruation is heavily associated with human females, and they have the most pronounced menstruation, it is also typical of [[ape]] relatives and [[monkey]]s.<ref name="Burton">{{cite book|vauthors=Burton FD|title=The Multimedia Guide to the Non-human Primates: Print Version|publisher=Prentice Hall Canada|isbn=978-0-13-209727-7|year=1995|page=290|url=https://books.google.com/books?id=hqNFAQAAIAAJ|access-date=June 5, 2018|archive-date=March 10, 2021|archive-url=https://web.archive.org/web/20210310000719/https://books.google.com/books?id=hqNFAQAAIAAJ|url-status=live}}</ref><ref name="Martin">{{cite book|vauthors=Martin R|title=How We Do It: The Evolution and Future of Human Reproduction|publisher=[[Basic Books]]|isbn=978-0-465-03015-6|year=2013|page=27|url=https://books.google.com/books?id=Up8WBQAAQBAJ&pg=PA27|access-date=June 5, 2018|archive-date=July 3, 2019|archive-url=https://web.archive.org/web/20190703211400/https://books.google.com/books?id=Up8WBQAAQBAJ&pg=PA27|url-status=live}}</ref> Female [[macaques]] menstruate, with a cycle length over the course of a lifetime that is comparable to that of female humans. Estrogens and [[progestogen]]s in the [[Menstruation (mammal)|menstrual cycles]] and during premenarche and postmenopause are also similar in female humans and macaques; however, only in macaques does keratinization of the epithelium occur during the [[follicular phase]].<ref name="Sarmento"/> The vaginal pH of macaques also differs, with near-neutral to slightly alkaline median values and is widely variable, which may be due to its lack of lactobacilli in the vaginal flora.<ref name="Sarmento"/> This is one reason why, although macaques are used for studying HIV transmission and testing [[microbicides]],<ref name="Sarmento"/> animal models are not often used in the study of sexually transmitted infections, such as trichomoniasis. Another is that such conditions' causes are inextricably bound to humans' genetic makeup, making results from other species difficult to apply to humans.<ref name="Kumar">{{cite book|vauthors=Kumar B, Gupta S|title=Sexually Transmitted Infections - E-book|publisher=[[Elsevier Health Sciences]]|isbn=978-81-312-2978-1|year=2014|page=1286|url=https://books.google.com/books?id=kQ9tAwAAQBAJ&pg=PA1286|access-date=January 14, 2018|archive-date=July 4, 2019|archive-url=https://web.archive.org/web/20190704044853/https://books.google.com/books?id=kQ9tAwAAQBAJ&pg=PA1286|url-status=live}}</ref>