Clitoris

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Clitoris
Clitoris anatomy labeled-en.svg
The internal anatomy of the human vulva, with the clitoral hood and labia minora indicated as lines. The clitoris extends from the visible portion to a point below the pubic bone.
Gray'ssubject #270 1266
ArteryDorsal artery of clitoris, deep artery of clitoris
VeinSuperficial dorsal veins of clitoris, deep dorsal vein of clitoris
NerveDorsal nerve of clitoris
PrecursorGenital tubercle
MeSHClitoris
Dorlands/ElsevierClitoris
 
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Clitoris
Clitoris anatomy labeled-en.svg
The internal anatomy of the human vulva, with the clitoral hood and labia minora indicated as lines. The clitoris extends from the visible portion to a point below the pubic bone.
Gray'ssubject #270 1266
ArteryDorsal artery of clitoris, deep artery of clitoris
VeinSuperficial dorsal veins of clitoris, deep dorsal vein of clitoris
NerveDorsal nerve of clitoris
PrecursorGenital tubercle
MeSHClitoris
Dorlands/ElsevierClitoris

The clitoris (Listeni/ˈklɪtərɨs/, Listeni/klɨˈtɔərɨs/, or UK /ˈkltɒrɨs/) is a female sexual organ present in mammals, ostriches and a limited number of other animals.[1] In humans, the visible button-like portion is near the front junction of the labia minora (inner lips), above the opening of the urethra. Unlike the penis, the male variant of the clitoris, it usually does not contain the distal portion or opening of the urethra and is therefore not used for urination. The spotted hyena, which has a particularly well-developed clitoris, is the only species in which the female urinates, mates and gives birth via the clitoris. Other carnivorous animals, and some mammals such as apes, rabbits, and spider monkeys, also have a well-developed clitoris.[2]

The clitoris is the human female's most sensitive erogenous zone and the primary source of female sexual pleasure.[3][4][5] In humans and other mammals, it develops from an outgrowth in the embryo called the genital tubercle. Initially undifferentiated, the tubercle develops into either a penis or a clitoris, depending on the presence or absence of the protein tdf, which is codified by a single gene on the Y chromosome. The clitoris is a complex structure, and its size and sensitivity can vary. The glans (head) of the human clitoris is roughly the size and shape of a pea, and is estimated to have more sensory nerve endings than any other part of the human body.[5][6]

Extensive sociological, sexological and medical debate have focused on the clitoris, primarily concerning anatomical accuracy, orgasmic factors and their physiological explanation for the G-Spot, and whether the clitoris is vestigial, an adaptation, or serves a reproductive function.[4][7][8][9] Social perceptions of the clitoris range from the significance of its role in female sexual pleasure, assumptions about its true size and depth, and varying beliefs regarding genital modification such as clitoris enlargement, clitoris piercing and clitoridectomy. Genital modification may be for aesthetic, medical or cultural reasons.[10][11][12] Cultural perceptions also impact on knowledge of the clitoris. Studies suggest that knowledge of its existence and anatomy is scant in comparison to that of other sexual organs, and that more education about it could help alleviate social stigmas associated with the female body and female sexual pleasure; for example, that the clitoris – and the vulva in general – are visually unappealing; that female masturbation is taboo; or that women's orgasms are something that "men are expected to master and control".[11][13]

Contents

Pronunciation and etymology

The Oxford English Dictionary gives the pronunciation /ˈkltɒrɨs/ for British English, adding that the word likely has its origin in the Ancient Greek κλειτορίς, kleitoris, perhaps derived from the verb κλείειν, kleiein, "to shut". It also states that the shortened form "clit", the first occurrence of which was noted in the United States, has been used in print since 1958: until then, the common abbreviation was "clitty".[14] Clitoris is also Greek for the word key, "indicating that the ancient anatomists considered it the key" to female sexuality.[15][16] In addition to key, the Online Etymology Dictionary suggests other Greek candidates for the word's etymology include a noun meaning "latch", "hook"; a verb meaning "to touch or titillate lasciviously", "to tickle" (one German synonym for the clitoris is der Kitzler, "the tickler"), although this verb is more likely derived from "clitoris"; and a word meaning "side of a hill", from the same root as "climax".[17]

The plural forms are clitorises in English and clitorides in Latin. The Latin genitive is clitoridis, as in "glans clitoridis". In medical and sexological literature, the clitoris is sometimes referred to as "the female penis" or pseudo-penis,[18] and the term clitoris is commonly used to refer to the glans alone;[4] partially because of this, there have been various terms for the organ that have historically confused its anatomy (see below).

Anatomy and structure

Embryonic development

Sexual differentiation begins about eight or nine weeks after conception,[19][20] and, in mammals, is determined by the sperm that carries either an X or a Y (male) chromosome.[21] The Y chromosome contains a sex-determining gene (SRY) that codifies for the protein tdf (testis determining factor) and triggers the creation of testosterone and Anti-Müllerian hormone for the embryo's development into a male.[19][22]

The formations that happen during the development of the urinary and reproductive organs make the male and female sex organs generally homologous (different versions of the same structure). The initially undifferentiated genital tubercle, a phallic outgrowth in the embryo, develops into either a clitoris or penis depending on exposure to androgens (male hormones). If exposed to testosterone, the genital tubercle enlarges and the preexisting phallus becomes a penis. By fusion of the genital folds, the urogenital sinus closes completely and forms the spongy urethra, and the genital swellings unite to form the scrotum.[19] In the absence of testosterone, the genital tubercle allows for formation of the clitoris; the initially rapid growth of the phallus gradually slows, and the clitoris is formed; it forms from the same tissues that become the glans and upper shaft of the penis.[19][23] The urogenital sinus persists as the vestibule of the vagina, the two genital folds form the labia minora, and the genital swellings enlarge to form the labia majora, completing the female genitalia.[19][20] A rare condition that can develop from higher than average androgen exposure is clitoromegaly (see below).[24][25] Some sources state that sexual differentiation continues until the 12th week,[26] while others state that it is clearly evident by the 13th week and that the sex organs are fully developed by the 16th week,[27] or that embryo sex based on external genitalia can usually be identified by an ultrasound after 16–18 menstrual weeks.[28]

General structure

The clitoris is a complex structure, containing external and internal components. It consists of two erectile bodies known as the corpora cavernosa, two clitoral crura ("legs") and the vestibular or clitoral bulbs. These bulbs are more closely related to the clitoris than the vestibule because of the similarity of the trabecular and erectile tissue within the clitoris and bulbs, and the absence of trabecular tissue in other genital organs.[15][29][30] The two coporas forming the clitoral body are surrounded by thick fibro-elastic tunica albuginea (literally meaning "white covering," connective tissue). These corpora are separated incompletely from each other with a medial near a fibrous pectiniform septum. Each crura is attached to the corresponding ischial ramus: extensions of the copora beneath the descending pubic rami.[29][30][31] The vestibular bulbs lie close to the crura on either side of the vaginal opening; internally, they are beneath the labia majora. When engorged with blood, they cuff the vaginal opening and cause the vulva to expand outward.[29][30] Though some texts state that they surround the vaginal opening, this does not appear to be the case and tunica albuginea does not envelope the erectile tissue of the bulbs.[29][30]

Human vulva
Vulva labeled no tags.jpg
Human vulva stretched to show externally-visible features of the clitoris in relation to other components: 1. Clitoral hood (prepuce); 2. Clitoral glans; 3. Urethral orifice; 4. Vulval vestibule; 5. Labia minora; 6. Vaginal opening; 7. Labia majora (hair removed); 8. Perineum
MeSHVulva
Dorlands/Elseviervulva

The head or glans of the clitoris is usually the size and shape of a pea, although it is sometimes much larger or smaller. Projecting at the front of the labial commissure where the edges of the outer lips (labia majora) meet at the base of the pubic mound is the clitoral hood (prepuce), which in full or part covers the glans of the clitoris. The clitoral unit forms a wishbone-shaped structure. The corpus cavernosum, extending up to several centimeters before reversing direction and branching, results in an inverted "V" shape, which extends as a pair of "legs" (the crura).[29][30] The crura are the proximal portions of the arms of the wishbone, and they continue along the anterior aspect of each ischiopubic ramus for several centimeters, meeting in the midline as the body (or shaft) of the clitoris. The tip of the body bends anteriorly away from the pubis, ending at the glans of the clitoris.[30] Concealed behind the labia minora, the crura terminate with attachment to the pubic arch (according to some),[32] or follow interior to the labia minora to meet at the fourchette (according to others).[33]

The clitoral body and the crura can be 10 centimetres (3.9 in) or more in length with the body measuring 5–7 centimetres (2.0–2.8 in) in length.[29] Associated are the urethral sponge, perineal sponge, a network of nerves and blood vessels, suspensory ligaments, muscles and pelvic diaphragm.[23] The clitoris, vestibular bulbs, labia minora, and urethra consist of two histologically distinct types of vascular tissue, the first of which is trabeculated, erectile tissue present in the clitoris and the bulbs, which have large, dilated vascular spaces filled with blood and are spongy in appearance. In contrast, although the clitoral glans becomes engorged with blood upon sexual arousal, and erectile tissue is commonly defined as tissue that may become engorged with blood, some sources state that the clitoral glans and labia minora are composed of non-erectile tissue, in which the blood vessels are dispersed within a fibrous matrix with only a minimal amount of smooth muscle,[29] or that "[t]he glans is a midline, densely neural, non-erectile structure".[4] Yang et al. challenge the conclusion that the glans is not formed of erectile tissue, stating that their dissections clearly show glanular vascular spaces, although not as prominent as those in the corpora. "The erectile tissue of the glans is slightly different from that of the body and crura. The vascular spaces are separated more by smooth muscle than in the body and crura," they concluded. "There is a thick layer of supporting tissue between the epithelium and the vascular spaces. In the epithelium and supporting tissue, there is a dense distribution of nerves and sensory receptors."[30] With regard to the urethral lumen, they state that it is surrounded by spongy tissue and that the tissue "is grossly distinct from the vascular tissue of the clitoris and bulbs, and on macroscopic observation, is paler than the dark tissue of the bulbs and clitoris. The bulbs arch over the distal urethra, outlining what might be appropriately called the 'bulbar urethra' in women".[30]

The glans of the clitoris, or the clitoris as a whole, is estimated to have around 8,000 sensory nerve endings – more than any other part of the human body.[5][6][34] There is considerable variation in how much of the clitoris protrudes from the hood and how much is covered by it, ranging from complete, covered invisibility to full, protruding visibility. A 1992 article in Obstetrics & Gynecology gives the average width of the clitoral glans as between 2.5 and 4.5 millimetres (0.098 to 0.18 in), with the average size as smaller than a pencil-top eraser, and the total clitoral length including glans and body as 16.0 +/- 4.3 mm.[35] The authors concluded that there is no identified correlation between the size of a clitoris and a woman's age, height, weight, use of hormonal contraception, or being post-menopausal, although women who had given birth had significantly larger measurements.[35]

Tissue from the clitoris may extend into the vagina's anterior wall.[4] Clitoral tissue is composed of large vascular spaces with mainly vascular epithelium and smooth muscle interspersed throughout, and the erectile tissue's trabecular nature allows engorgement and expansion during sexual arousal.[29][30] "Histological evaluation of the clitoris, especially of the corpora cavernosa, is incomplete because for many years the clitoris was considered a rudimentary and nonfunctional organ," stated researcher Atilla Şenaylı. "Baskin and colleagues evaluated the masculinized clitoris after dissection and put the serial dissected specimens together using imaging software after Masson chrome staining." This revealed that the nerves of the clitoris surround the whole corpus. It is "known that the subalbugineal layer between the erectile tissue and tunica albuginea is absent in the clitoris, but desmin and vimentin immunoreactivity evaluations in arterial and vein muscle cells of the clitoris are not clear from previous reports".[31]

Clitoral and penile similarities and differences

The clitoris and penis are generally the same anatomical structure, although the distal portion or opening of the urethra is absent in the clitoris of humans and most other animals. The first researcher to refer to the human penis as essentially an enlarged clitoris was the anatomist and sexologist Josephine Lowndes Sevely in 1987.[36][37] The clitoris displays a hood that is the equivalent of the penis's foreskin, which covers the glans, and a shaft that is attached to the glans. The male corpora cavernosa (spongy tissue surrounding the male urethra) are homologous to the body of the clitoris; the corpus spongiosum is homologous to the vestibular bulbs beneath the labia minora, and the scrotum is homologous to the labia minora and labia majora.[23][38][39] Upon anatomical study, the penis can be described as a clitoris that has been mostly pulled out of the body and grafted on top of a significantly smaller piece of spongiosum containing the urethra.[38][39] Contrasting the human clitoris's estimated 8,000 nerve endings (for its glans or clitoral body as a whole), the human penis or glans penis is estimated to have around 4,000,[5][6][34] though some sources state that there are as many in the clitoral glans as there are in the glans penis or the penis as a whole,[40][41] or debate whether the uncircumcised penis has thousands more than the circumcised penis.[42][43][44][45]

At the tip of the clitoral body, the glans of the clitoris rests as a fibrovascular cap. Some scholars assert that in contrast to the glans of the penis, the glans of the clitoris lacks smooth muscle within its fibrovascular cap, and is thus differentiated from the erectile tissues of the clitoris and bulbs.[29] Additionally, bulb size varies and may be dependent on age and estrogenization.[29] Though the bulbs are considered the equivalent of the male spongiosum, they do not completely encircle the urethra.[29]

Internally, the penis is composed of two kinds of tissue. The thin corpus spongiosum runs along the underside of the shaft, enveloping the urethra, and expands at the end to form the glans. It partially contributes to erection, primarily by the two corpora cavernosa, which comprise the bulk of the shaft. The male corpora cavernosa taper off internally on reaching the spongiosum head.[46][47] Like the female cavernosa, the male cavernosa soak up blood and become erect when sexually excited.[46][47] While in women, the cavernosa are Y-shaped with three parts – crown, body, and legs – the body accounts for much more of the structure in men, and the legs are stubbier. Typically, the cavernosa are longer and thicker in males than in females.[30][48]

Sexual stimulation, findings and debates

General stimulation, practices, and arousal

Because the clitoris is homologous to the penis, it is the equivalent in its capacity to receive sexual stimulation.[49][50] The most effective sexual stimulation of the clitoris is usually through manual or oral stimulation, often referred to as direct clitoral stimulation.[50][51][52] Direct clitoral stimulation involves stimulation to the external anatomy of the clitoris (glans, hood, shaft, and the vulva due to its abundance of clitoral tissue).[4][53] Due to the glans's sensitivity, direct stimulation to it is not always pleasurable; instead, direct stimulation to the hood or the areas near the glans are often more pleasurable, with the majority of females preferring to use the hood to stimulate the glans, or to have the glans rolled between the lips of the labia, for indirect touch.[5][54] The majority of women also "enjoy a light caressing of the shaft of the clitoris" combined with the occasional circling of the clitoral glans, with or without manual penetration of the vagina, while others enjoy having the entire area of the vulva caressed.[5] As opposed to use of dry fingers, stimulation from fingers that have been well-lubricated, either by vaginal lubrication or a personal lubricant, is usually more pleasurable for the external areas of the clitoris.[5][55] Personal lubricant is especially necessary in cases where the clitoris is highly sensitive before sexual arousal or physical stimulation.[56]

As the clitoris's external location does not allow for direct stimulation by sexual penetration, any external clitoral stimulation while in the missionary position usually results from the pubic bone area, the movement of the groins when in contact. As such, some couples may engage in the woman-on-top position or the coital alignment technique, a technique combining the "riding high" variation of the missionary position with pressure-counterpressure movements performed by each partner in rhythm with sexual penetration, to maximize clitoral stimulation.[57][58][59] Lesbian couples may engage in tribadism for ample clitoral stimulation or for mutual clitoral stimulation during whole-body contact.[60][61][62] Pressing the penis or a dildo in a gliding or circular motion against the clitoris (intercrural sex), or stimulating it by movement against another body part, during any number of sex positions, may also be practiced.[63][64] A vibrator, or specifically a clitoral vibrator, or other sex toys, may be used during or absent of any of the aforementioned practices.[63][65]

During sexual arousal and orgasm, the clitoris and the whole of the genitalia engorge and change color as the erectile tissues fill with blood, and the individual experiences vaginal contractions.[30][66][67] With sexual arousal, the ischiocavernosus and bulbocavernosus muscles, which insert into the corpora cavernosa, "contract and compress the dorsal vein of the clitoris, the only vein that drains the blood from the spaces in the corpora cavernosa" and the arterial blood "continues to pour in and, having no way to drain out, fills the venous spaces until they become turgid and engorged with blood". It is this mechanism that "causes the stiffening and erection of the clitoris".[15] The glans doubles in diameter, and, upon further stimulation, it becomes less visible as it is covered by the swelling of tissues of the clitoral hood.[68][66] The swelling protects the glans from direct contact, as direct contact at this stage can be more irritating than pleasurable.[68][69] A short time after stimulation has stopped, especially if orgasm has been achieved, it becomes visible again and returns to its normal state,[70] with a few seconds (usually 5-10) to return to its normal position and 5–10 minutes to return to its original size.[68][71] Orgasm leads to a dispersal of the accumulated blood, but if orgasm is not achieved, the clitoris may remain engorged for a few hours, which individuals often find uncomfortable.[57][72] Additionally, the clitoris is very sensitive after orgasm, making further stimulation initially painful for some women.[73][72] Masters and Johnson documented the sexual response cycle, which has four phases and is still the clinically accepted definition of the human orgasm,[74][75][76] but knowledge of the measurement of physiologic parameters of sexual function in women is lacking "and far behind that in men".[31]

Clitoral and vaginal orgasmic factors and relationships

The majority of women, 70–80 percent for general statistics, require direct clitoral stimulation (consistent manual, oral, or other friction against the external parts of the clitoris) to achieve orgasm,[77][78][79] although indirect clitoral stimulation (for example, via vaginal penetration) may also be sufficient.[4][76][80] The area near the entrance of the vagina (the lower third) contains nearly 90 percent of the vaginal nerve endings, and there are areas in the anterior vaginal wall and between the top junction of the labia minora and the urethra that are especially sensitive, but intense sexual pleasure and orgasm from vaginal stimulation is occasional because the vagina has significantly fewer nerve endings than the clitoris.[41][81][82] Prominent debate over the quantity of vaginal nerve endings began with Alfred Kinsey, who was the first researcher to harshly criticize Sigmund Freud's theory that clitoral orgasms are a prepubertal or adolescent phenomenon and that vaginal (or G-Spot) orgasms are something that only physically mature females have.[8][83][84] Through his interviews with thousands of women,[85] Kinsey found that most women could not have vaginal orgasms.[83] He "criticized Freud and other theorists for projecting male constructs of sexuality onto women" and "viewed the clitoris as "the main center of sexual response". He considered the vagina to be "relatively unimportant" for sexual satisfaction, relaying that "few women inserted fingers or objects into their vaginas when they masturbated". Believing that vaginal orgasms are "a physiological impossibility" because the vagina has insufficient nerve endings for sexual pleasure or climax, he "concluded that satisfaction from penile penetration [is] mainly psychological or perhaps the result of referred sensation".[83]

Masters and Johnson's research, as well as Shere Hite's, generally supported Kinsey's findings about the female orgasm.[75][86] Masters and Johnson were the first to determine that the clitoral structures surround and extend along and within the labia. They observed that both clitoral and vaginal orgasms had the same stages of physical response, and found that the majority of their subjects could only achieve clitoral orgasms, while a minority achieved vaginal orgasms. On that basis, they argued that clitoral stimulation is the source of both kinds of orgasms,[74][75][87] reasoning that the clitoris is stimulated during penetration by friction against its hood.[88] The research came at the time of the second-wave feminist movement, which inspired feminists to reject the distinction made between clitoral and vaginal orgasms. Feminist Anne Koedt argued that because men "have orgasms essentially by friction with the vagina" and not the clitoral area, this is why women's biology had not been properly analyzed. "Today, with extensive knowledge of anatomy, with [C. Lombard Kelly], Kinsey, and Masters and Johnson, to mention just a few sources, there is no ignorance on the subject [of the female orgasm]. There are, however, social reasons why this knowledge has not been popularized. We are living in a male society which has not sought change in women's role," she stated in her 1970 article The Myth of the Vaginal Orgasm.[8]

Supporting an anatomical relationship between the clitoris and vagina is a study published in 2005, which investigated the size of the clitoris; Australian urologist Helen O'Connell, described as having initiated discourse among mainstream medical professionals to refocus on and redefine the clitoris, noted a direct relationship between the legs or roots of the clitoris and the erectile tissue of the "clitoral bulbs" and corpora, and the distal urethra and vagina while using MRI technology.[4][74][89] While some studies, using ultrasound, have found physiological evidence of the G-Spot in women who report having orgasms during intercourse,[90][91] O'Connell asserts that this interconnected relationship is the physiological explanation for the conjectured G-Spot and experience of vaginal orgasms, taking into account the stimulation of the internal parts of the clitoris during vaginal penetration. "The vaginal wall is, in fact, the clitoris," she explained. "If you lift the skin off the vagina on the side walls, you get the bulbs of the clitoris – triangular, crescental masses of erectile tissue."[4] O'Connell et al., after performing dissections on the female genitals of cadavers and using photography to map the structure of nerves in the clitoris, made the claim in 1998 that there is more erectile tissue associated with the clitoris than is generally described in anatomical textbooks, and were thus already aware that the clitoris is more than just its glans – the "little hill".[66] They reasoned that it is possible that some females have more extensive clitoral tissues and nerves than others, especially having observed this in young cadavers as compared to elderly ones,[66] and therefore whereas the majority of females can only achieve orgasm by direct stimulation of the external parts of the clitoris, the stimulation of the more generalized tissues of the clitoris via intercourse may be sufficient for others.[4]

French researchers Odile Buisson and Pierre Foldès reported similar findings to that of O'Connell's. In 2008, they published the first complete 3D sonography of the stimulated clitoris, and republished it in 2009 with new research, demonstrating the ways in which erectile tissue of the clitoris engorges and surrounds the vagina. On the basis of their findings, they argued that women may be able to achieve vaginal orgasm via stimulation of the G-Spot, because the highly innervated clitoris is pulled closely to the anterior wall of the vagina when the woman is sexually aroused and during vaginal penetration. They assert that since the front wall of the vagina is inextricably linked with the internal parts of the clitoris, stimulating the vagina without activating the clitoris may be next to impossible. In their 2009 published study, the "coronal planes during perineal contraction and finger penetration demonstrated a close relationship between the root of the clitoris and the anterior vaginal wall". Buisson and Foldès suggested "that the special sensitivity of the lower anterior vaginal wall could be explained by pressure and movement of clitoris's root during a vaginal penetration and subsequent perineal contraction".[80][92]

Researcher Vincenzo Puppo, who, while agreeing that the clitoris is the center of female sexual pleasure and believing that there is no anatomical evidence of the vaginal orgasm, disagrees with O'Connell and other researchers' terminological and anatomical descriptions of the clitoris (such as referring to the "vestibular bulbs" as the "clitoral bulbs") and states that "the inner clitoris" does not exist because the penis cannot come in contact with the congregation of multiple nerves/veins situated until the angle of the clitoris, detailed by Kobelt, or with the roots of the clitoris, which do not have sensory receptors or erogenous sensitivity, during vaginal intercourse.[18] In contrast, the majority of researchers maintain that vaginal orgasms are the result of clitoral stimulation, reaffirming that clitoral tissue extends even in the area most commonly reported to be the G-Spot.[9][93][94] Researcher Amichai Kilchevsky believes that the G-Spot is analogous to the base of the male penis. He argues that because humans all start out as female in the womb, and therefore the penis is essentially a clitoris enlarged by male hormones, there is no evolutionary reason why females would have an entity in addition to the clitoris that can produce orgasms.[94] Arguments that vaginal orgasms help encourage sexual intercourse in order to facilitate reproduction are challenged by the fact that vaginal orgasms are significantly difficult to achieve,[9][76] a predicament that is believed to be the result of nature easing the process of child bearing by drastically reducing the number of vaginal nerve endings.[95] However, supporting a distinct G-Spot is a study by Rutgers University, published in 2011, which was the first to map the female genitals onto the sensory portion of the brain;[96] brain scans showed that the brain registered distinct feelings between stimulating the clitoris, the cervix and the vaginal wall – where the G-Spot is reported to be – when several women stimulated themselves in a functional magnetic resonance (fMRI) machine.[96] "I think that the bulk of the evidence shows that the G-Spot is not a particular thing," stated Barry Komisaruk, head of the research findings. "It's not like saying, 'What is the thyroid gland?' The G-Spot is more of a thing like New York City is a thing. It's a region, it's a convergence of many different structures."[9]

A pulled-out clitoral glans.

Historical and modern perceptions

Existence, illustration accuracy and vernacular

Although for more than 2,500 years there were scholars who considered the clitoris and the penis equivalent in all respects except their arrangement,[97] the clitoris was also subject to "discovery" and "rediscovery" through empirical documentation by male scholars, due to "the frequent omission or misrepresentation of the organ in historical and contemporary anatomical texts".[4][29][98] The ancient Greeks and Romans up to and throughout the Renaissance were aware that male and female sex organs are anatomically similar,[99][100] but prominent anatomists, notably Galen (129 AD – 200 AD) and Vesalius (1514–1564), regarded the vagina as the structural equivalent of the penis, except for being inverted. Vesalius argued against the existence of the clitoris in normal women, and his anatomical model showing how the penis corresponds with the vagina displayed no role for the clitoris.[4] Ancient Greek and Roman sexuality additionally designated penetration as "male-defined" sexuality. The term tribas, or tribade, was used to refer to a woman or intersex individual who actively penetrated another person (male or female) through use of the clitoris or a dildo. As any sexual act was believed to require that one of the partners be "phallic" and that therefore sex between women was impossible without this feature, popular mythology pictured lesbians as either having enlarged clitorises or as incapable of sexual enjoyment without the substitution of a phallus.[101][102]

In 1545, Charles Estienne was the first writer to identify the clitoris in a work based on dissection, but he concluded that it had a urinary function.[4] Following this study, Realdo Colombo (also known as Matteo Renaldo Colombo), a lecturer in surgery at the University of Padua, Italy, published a book called De re anatomica in 1559,[17][103] in which he describes the "seat of woman's delight". In his role as researcher, Colombo concluded, "Since no one has discerned these projections and their workings, if it is permissible to give names to things discovered by me, it should be called the love or sweetness of Venus."[6][17] Colombo's claim was disputed by his successor at Padua, Gabriele Falloppio (who discovered the fallopian tube), who claimed that he was the first to discover the clitoris. In 1561, Falloppio stated, "Modern anatomists have entirely neglected it ... and do not say a word about it ... and if others have spoken of it, know that they have taken it from me or my students." This caused an upset in the European medical community. Having read Colombo and Falloppio's detailed descriptions of the clitoris, Vesalius stated, "It is unreasonable to blame others for incompetence on the basis of some sport of nature you have observed in some women and you can hardly ascribe this new and useless part, as if it were an organ, to healthy women." He concluded, "I think that such a structure appears in hermaphrodites who otherwise have well formed genitals, as Paul of Aegina describes, but I have never once seen in any woman a penis (which Avicenna called albaratha and the Greeks called an enlarged nympha and classed as an illness) or even the rudiments of a tiny phallus."[4]

It was difficult for the average anatomist to argue against Galen or Vesalius's research. Galen was the most famous physician of the Greek era and his works were considered the standard of medical understanding up to and throughout the Renaissance (i.e. for almost two millennia),[4][100] and various terms being used to describe the clitoris seemed to have further confused the issue of its structure. In addition to Avicenna's naming it the albaratha or virga (rod) and Colombo's calling it sweetness of Venus, Hippocrates used the term columella (little pillar), and Albucasis, an Arabic medical authority, named it tentigo (tension). The names indicated that each description of the structures was about the body and glans of the clitoris, but usually the glans.[4] It was additionally known to the Romans, who named it (vulgar slang) landica.[104] However, Albertus Magnus, one of the most prolific writers of the Middle Ages, emphasized the "homologies between male and female structures and function" by adding "a psychology of sexual arousal" not found in Aristotle's descriptions of the clitoris. Magnus devoted "equal space to his description of the male and female—whereas in Constantine's treatise Liber de coitu, references to the female are quite incidental." Like Avicenna, Magnus also used the word virga for the clitoris, but employed it for the male and female genitals.[4] Despite Magnus's efforts to give equal ground to the clitoris, the cycle of suppression and rediscovery of the organ continued, and a 16th-century justification for clitoridectomy appears to have been confused by hermaphroditism and the imprecision created by the word nymphae substituted for the word clitoris. Nymphotomia was a medical operation to excise an unusually large clitoris, but what was considered "unusually large" was often a matter of perception. The procedure was routinely performed on Egyptian women,[4][105][106] due to physicians such as Jacques Daléchamps who believed that this version of the clitoris was "an unusual feature that occurred in almost all Egyptian women [and] some of ours, so that when they find themselves in the company of other women, or their clothes rub them while they walk or their husbands wish to approach them, it erects like a male penis and indeed they use it to play with other women, as their husbands would do ... Thus the parts are cut".[4]

Caspar Bartholin, a 17th-century Danish anatomist, dismissed Colombo and Falloppio's claims that they discovered the clitoris, arguing that the clitoris had been widely known to medical science since the second century.[107] Although 17th-century midwives recommended to men and women that women should aspire to achieve orgasms to help them get pregnant for general health and well-being and to keep their relationships healthy,[100] debate about the importance of the clitoris persisted, notably in the work of Regnier de Graaf in the 17th century,[108] and Georg Ludwig Kobelt in the 19th.[4][109] Like Falloppio and Bartholin, De Graaf criticized Columbo's claim of having discovered the clitoris; his work, taking place in the 17th century, appears to have provided the first comprehensive account of clitoral anatomy. "We are extremely surprised that some anatomists make no more mention of this part than if it did not exist at all in the universe of nature," he stated. "In every cadaver we have so far dissected we have found it quite perceptible to sight and touch." De Graaf emphasized the need to distinguish nympha from clitoris, choosing to "always give [the clitoris] the name clitoris" to avoid confusion; this resulted in frequent use of the correct name for the organ among anatomists, but considering that nympha was also varied in its use and eventually became the term specific to the labia minora, more confusion ensued.[4] Debate about whether orgasm was even necessary for women began in the Victorian era, and Freud's 1905 theory about the immaturity of clitoral orgasms (see above) negatively affected women's sexuality throughout most of the 20th century.[100][110] From the 18th – 20th century, especially during the 20th, details of the clitoris from various genital diagrams presented in earlier centuries were omitted from later texts.[4][29][97][100]

O'Connell (2005) describes typical textbook descriptions of the clitoris as lacking detail and including inaccuracies, such as older and modern anatomical descriptions of the female human urethral and genital anatomy having been based on dissections performed on elderly cadavers whose erectile (clitoral) tissue had shrunk.[66] She instead credits the work of Georg Ludwig Kobelt as the most comprehensive and accurate description of clitoral anatomy.[4] The full extent of the clitoris was additionally alluded to by Masters and Johnson in 1966, but in such a muddled fashion that the significance of their description became obscured. In 1981, the Federation of Feminist Women's Health Clinics (FFWHC) continued this process with anatomically precise illustrations identifying 18 structures of the clitoris,[4][5][100] although these works did not have an impact on anatomical texts until O'Connell's research.[89] MRI measurements, which provide a live and multi-planar method of examination, now complement these efforts, showing that the volume of clitoral erectile tissue is ten times that which is shown in doctors' offices and in anatomy text books.[89]

In 2000, researchers Shirley Ogletree and Harvey Ginsberg concluded that there is a general neglect of the word clitoris in common vernacular. They looked at the terms used to describe genitalia in the PsycINFO database from 1887 to 2000 and found that penis was used in 1,482 sources, vagina in 409, while clitoris was only mentioned in 83. They additionally analyzed 57 books listed in a computer database for sex instruction. In the majority of the books, penis was the most commonly discussed body part – mentioned more than clitoris, vagina, and uterus put together. They last investigated terminology used by college students, ranging from Euro-American (76%/76%), Hispanic (18%/14%), and African American (4%/7%), regarding their beliefs about sexuality and knowledge on the subject. The students were overwhelmingly educated to believe that the vagina is the female counterpart to the penis. The authors found that the students' belief that the inner portion of the vagina is the most sexually sensitive part of the female body correlated with negative attitudes toward masturbation and strong support for sexual myths.[11] A 2005 study reported similar, finding that among a sample of undergraduate students, the most frequently cited sources for knowledge about the clitoris were school and friends, and that this was associated with the least amount of tested knowledge. Knowledge of the clitoris by self-exploration was the least cited, but "respondents correctly answered, on average, three of the five clitoral knowledge measures". The authors stated, "Knowledge correlated significantly with the frequency of women's orgasm in masturbation but not partnered sex. Our results are discussed in light of gender inequality and a social construction of sexuality, endorsed by both men and women, that privileges men's sexual pleasure over women's, such that orgasm for women is pleasing, but ultimately incidental." They concluded that part of the solution to remedying "this problem" requires that males and females are taught more about the clitoris than is currently practiced.[13]

Modification and mutilation

An enlarged clitoris due to clitoromegaly.

Motivations for clitoral modification and mutilation vary, as well as their effects on sexual stimulation. One modification is clitoris enlargement, which may be intentional or unintentional.[25][31][111][112] Those taking hormones or other medications as part of female-to-male transition usually experience dramatic clitoral growth; individual desires and the difficulties of phalloplasty (construction of a penis) often result in the retention of the original genitalia with the enlarged clitoris as a penis analogue.[31][111][112] However, the clitoris cannot reach the size of the penis through hormones.[112] Surgery to add function to the clitoris, such as metoidioplasty or clitoral release, are alternatives to phalloplasty that permit retention of sexual sensation in the clitoris.[111] Use of anabolic steroids by bodybuilders and other athletes can also result in significant enlargement of the clitoris in concert with other masculinizing effects on their bodies.[25]

The clitoris may be partially or completely removed during female genital mutilation (FGM), also known as a clitoridectomy, female circumcision, or female genital cutting (FGC).[113][114] This has existed at one point or another in almost all human civilizations,[105] usually to exert control over the sexual behavior, including masturbation, of girls and women, but also to change the clitoris's appearance.[105][106][114][115] It is carried out in several countries, especially in Africa, with 85% of genital mutilations performed in Africa consisting of clitoridectomy or excision,[106] and to a lesser extent in the Middle East and Southeast Asia, on girls from a few days old to mid adolescent, often to reduce sexual desire in an effort to preserve vaginal virginity.[105][106][114] In the United States, it is sometimes practiced on girls "born with a larger than normal clitoris".[113] Custom and tradition are the most frequently cited reasons for FGM, with some cultures believing that not performing it has the possibility of disrupting the cohesiveness of their social and political systems, such as FGM also being a part of a girl's initiation into adulthood. Often, a girl is not considered an adult in a FGM-practicing society unless she has undergone FGM, and the "removal of the clitoris and labia – viewed by some as the male parts of a woman's body – is thought to enhance the girl's femininity, often synonymous with docility and obedience".[106][114] Some authors believe that it was also "practiced in ancient Egypt as a sign of distinction among the aristocracy, and have reported that traces of infibulation can be found on Egyptian mummies".[105] Amnesty International estimates that more than two million FGM procedures are performed every year.[106]

Removing the glans of the clitoris does not mean that the whole structure is lost, since the clitoris reaches deep into the genitals.[4] The largest group requiring surgical genital correction are females with adrenogenital syndrome. Researcher Atilla Şenaylı stated, "The main expectations for the operations are to create a normal female anatomy, with minimal complications and improvement of life quality. Cosmesis, structural integrity, and coital capacity of the vagina, and absence of pain during sexual activity are the parameters to be judged by the surgeon." Atilla added that although "expectations can be standardized within these few parameters, operative techniques have not yet become homogeneous. Investigators have preferred different operations for different ages of patients".[31] Gender assessment and surgical treatment are the two main steps in intersex operations. "The first treatments for clitoromegaly were simply resection of the clitoris. Later, it was understood that the clitoris glans and sensory input are important to facilitate orgasm," stated Atilla. "The epithelium of the glans clitoridis has high cutaneous sensitivity, which is important in sexual responses. Therefore, recession clitoroplasty was later devised as an alternative, but reduction clitoroplasty is the method currently performed. In this operation, the glans is preserved and parts of the erectile bodies are excised." Problems with the technique, include loss of sensation, sexual function, and sloughing of the glans.[31] One way to preserve the organ with its innervations and function is to imbricate and bury the glans clitoris: "although pain during stimulus because of trapped tissue under the scarring is nearly routine. In another method, 50 percent of the ventral clitoris is removed through the level base of the clitoral shaft, and it is reported that good sensation and clitoral function are observed in follow up. However, it has also been reported that the complications are from the same as those in the older procedures for this method".[31]

What is often referred to as "clit piercing" is actually the more common (and significantly less complicated) clitoral hood piercing. Since clitoral piercing is difficult and very painful, piercing of the clitoral hood is more common than piercing the clitoral shaft, owing to the small percentage of people who are anatomically suited for it; furthermore, most piercing artists are reluctant to attempt such a delicate procedure.[12][116] This is especially the case in the United States; in various cultures, however, the clitoris is sometimes pierced directly.[12][116] Clitoral piercing or clitoral hood piercing are sometimes channeled in the form of horizontal and vertical piercings. The triangle is a very deep horizontal hood piercing, and is done behind the clitoris as opposed to in front of it. Some styles, such as the Isabella, pass through the clitoris but are placed deep at the base, where they provide unique stimulation; they still require the proper genital build, but are more common than general shaft piercings.[12][116]

Vestigiality, adaptionist and reproductive views

Whether the clitoris is vestigial, an adaptation, or serves a reproductive function has also been debated.[117][118] Geoffrey Miller states that Helen Fisher, Meredith Small and Sarah Blaffer Hrdy "have viewed the clitoral orgasm as a legitimate adaptation in its own right, with major implications for female sexual behavior and sexual evolution".[119] Like Lynn Margulis and Natalie Angier, Miller believes, "The human clitoris shows no apparent signs of having evolved directly through male mate choice. It is not especially large, brightly colored, specifically shaped or selectively displayed during courtship." He contrasts this with other female species such as spider monkeys and spotted hyenas that have clitorises as long as their male counterparts. He suggests that the human clitoris "could have evolved to be much more conspicuous if males had preferred sexual partners with larger brighter clitorises and that its "inconspicuous design combined with its exquisite sensitivity suggests that the clitoris is important not as an object of male mate choice, but as a mechanism of female choice".[119] Although Miller states that male scientists such as Stephen Jay Gould and Donald Symons "have viewed the female clitoral orgasm as an evolutionary side-effect of the male capacity for penile orgasm" and that they "suggested that clitoral orgasm cannot be an adaptation because it is too hard to achieve,"[119] Gould acknowledged that "most female orgasms emanate from a clitoral, rather than vaginal (or some other), site" and that his nonadaptive belief "has been widely misunderstood as a denial of either the adaptive value of female orgasm in general, or even as a claim that female orgasms lack significance in some broader sense". He explained that although he accepts that "clitoral orgasm plays a pleasurable and central role in female sexuality and its joys," "[a]ll these favorable attributes, however, emerge just as clearly and just as easily, whether the clitoral site of orgasm arose as a spandrel or an adaptation". He said that the "male biologists who fretted over [the adaptionist questions] simply assumed that a deeply vaginal site, nearer the region of fertilization, would offer greater selective benefit" due to their Darwinian, summum bonum beliefs about enhanced reproductive success.[120]

Similar to Gould's beliefs about adaptionist views and that "females grow nipples as adaptations for suckling, and males grow smaller unused nipples as a spandrel based upon the value of single development channels,"[120] Elisabeth Lloyd suggests that there is little evidence to support an adaptionist account of female orgasm.[76][118] "Lloyd views female orgasm as an ontogenetic leftover; women have orgasms because the urogenital neurophysiology for orgasm is so strongly selected for in males that this developmental blueprint gets expressed in females without affecting fitness, just as males have nipples that serve no fitness-related function," stated Meredith L. Chivers.[118] At the 2002 conference for Canadian Society of Women in Philosophy, Dr. Nancy Tuana asserted that the clitoris is unnecessary in reproduction; she states that it has been ignored because of "a fear of pleasure. It is pleasure separated from reproduction. That's the fear". She reasoned that this fear causes ignorance, which veils female sexuality.[87] O'Connell said, "It boils down to rivalry between the sexes: the idea that one sex is sexual and the other reproductive. The truth is that both are sexual and both are reproductive." She reiterates that the bulbs appear to be part of the clitoris and that the distal urethra and vagina are intimately related structures, although they are not erectile in character, forming a tissue cluster with the clitoris that appears to be the locus of female sexual function and orgasm.[4][30]

In other animals

With a urogenital system in which the female urinates, mates and gives birth via an enlarged, erectile clitoris, the spotted hyena is the only mammalian species devoid of an external vaginal opening.[121]

Although the clitoris is present in most mammals,[122][123] few detailed studies of the anatomy of the clitoris in non-human animals exist.[124] The clitoris is especially developed in apes, lemurs, rabbits, and some carnivorous animals, and, like the penis, often contains a small bone, the os clitoridis.[122][125] In the lemming and a few other animals, it has an interior passage, or urethra, making it almost identical to the penis. In kangaroos and opossum, the clitoris is split, like the glans in their male counterparts. In the spider monkey, the clitoris is very similar to the penis, being three or four inches long and providing a glans and prepuce. All female galagos (bush babies) have a long pendulous clitoris. Because spider monkeys of South America have pendulous and erectile clitorises long enough to be mistaken for a penis, researchers and observers of the species look for a scrotum to determine the animal's sex. A similar approach is to identify scent-marking glands that may also be present on the clitoris.[122][126]

Female spotted hyenas have a phallus 90 percent as long and the same diameter as a male penis (171 millimeters long and 22 millimeters in diameter).[127] They have a highly erectile clitoris, complete with a false scrotum, and "the resemblance to male genitalia is so close that sex can be determined with confidence only by palpitation of the scrotum".[128] This pseudo-penis can also be distinguished from the males' genitalia by its greater thickness and more rounded glans.[121] The female possesses no external vagina, as the labia are fused to form a pseudo-scrotum. In the females, this scrotum consists of soft adipose tissue.[128][129][130] The hyena's clitoris "extends away from the body in a sleek and slender arc, measuring, on average, over 17 cm from root to tip. Just like a penis, [it] is fully erectile, raising its head in hyena greeting ceremonies, social displays, games of rough and tumble or when sniffing out peers. Just like the male, the female has small penile spines on the glans, or head, of her clitoris, making the clitoris tip feel like soft sandpaper".[130][131] Unlike any other female species, the urethra and vagina of the hyena exit through the clitoris, and the females thus copulate and give birth through this organ.[128][131][132] This trait makes mating more laborious for the male than in other mammals, and also makes rape impossible.[129][130] Because the clitoris of the hyena is higher on the belly than the vagina in most mammals, the male hyena "must slide his rear under the female when mating so that his penis lines up with [her clitoris]". In an action similar to pushing up a shirtsleeve, the "female retracts the [pseudo-penis] on itself, and creates an opening into which the male inserts his own penis".[127]

The formation of the hyena's pseudo-penis appears largely androgen-independent, as the pseudo-penis appears in the female fetus before differentiation of the fetal ovary and adrenal gland.[121] After giving birth, the pseudo-penis is stretched and loses much of its original aspects; it becomes a slack-walled and reduced prepuce with an enlarged orifice with split lips.[133] "About 25% of the females die during their first birth, and [others] lose over 60% of their firstborn young."[127] A 2006 Baskina et al. study concluded, "The basic anatomical structures of the corporeal bodies in both sexes of humans and spotted hyenas were similar. As in humans, the dorsal nerve distribution was unique in being devoid of nerves at the 12 o'clock position in the penis and clitoris of the spotted hyena" and that "[d]orsal nerves of the penis/clitoris in humans and male spotted hyenas tracked along both sides of the corporeal body to the corpus spongiosum at the 5 and 7 o'clock positions. The dorsal nerves penetrated the corporeal body and distally the glans in the hyena" and, in female hyenas, "the dorsal nerves fanned out laterally on the clitoral body. Glans morphology was different in appearance in both sexes, being wide and blunt in the female and tapered in the male".[132]

Researchers studying the peripheral and central afferent pathways from the feline clitoris concluded that "Afferent neurons projecting to the clitoris of the cat were identified by WGA-HRP tracing in the S1 and S2 dorsal root ganglia. An average of 433 cells were identified on each side of the animal. 85 percent and 15 percent of the labeled cells were located in the S1 and S2 dorsal root ganglia, respectively. The average cross sectional area of clitoral afferent neuron profiles was 1.479±627 μm2." They also stated that light "constant pressure on the clitoris produced an initial burst of single unit firing (maximum frequencies 170–255 Hz) followed by rapid adaptation and a sustained firing (maximum 40 Hz), which was maintained during the stimulation. Tonic firing increased to an average maximum of 145 Hz at 6–8 g/mm2 pressure" and "[t]hese results indicate that the clitoris is innervated by mechano-sensitive myelinated afferent fibers in the pudental nerve which project centrally to the region of the dorsal commissure in the L7-S1 spinal cord".[134]

The external phenotype and reproductive behavior of 21 freemartin sheep and two male pseudohermaphrodite sheep were recorded with the aim of identifying any characteristics that could predict a failure to breed. Among things recorded were the size and shape of the vulva and clitoris, the length of the vagina, the size of the teats, the presence or absence of inguinal gonads, and the ultrasonographic characteristics of the inguinal gonads: "A subjective assessment of the masculinity of each animal's body form was also made, and its behavioural responses to a virile ram and to an oestrus ewe were recorded. A number of physical and behavioural abnormalities were detected but the only consistent finding in all 23 animals was a short vagina which varied in length from 3.1 to 7.0 cm, compared with 10 to 14 cm in normal animals."[135] In a study documenting the clitoral structure of mice, it was found that the mouse perineal urethra is surrounded by erectile tissue forming the bulbs of the clitoris, similar to the anatomy of human females:[124] "In the mouse, as in human females, tissue organization in the corpora cavernosa of the clitoris is essentially similar to that of the penis except for the absence of a subalbugineal layer interposed between the tunica albuginea and the erectile tissue."[124]

See also

References

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Bibliography

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