The clitoris is a sexual organ that is present only in female mammals. In humans, the visible button-like portion is located near the anterior junction of the labia minora, above the opening of the urethra and vagina. Unlike the penis, which is homologous to the clitoris, the clitoris does not contain the distal portion of the urethra, and functions solely to induce sexual pleasure. The only known exception to this is in the Spotted Hyena. In this species, the urogenital system is unique in that the female urinates, mates and gives birth via an enlarged, erectile clitoris, known as a pseudo-penis.
The clitoris is a complex structure that includes external and internal components. Projecting at the front of the vaginal 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 head (clitoral glans) -- commonly about the size and shape of a shirt-button. Following from the head back and up along the shaft, it is found that this extends up to several centimeters before reversing direction, branched resulting in a shaped like an inverted "V", and extending as a pair of "legs" known as the clitoral crura formed of the corpora cavernosa, which are concealed behind the labia minora, and terminating attached to the pubic arch, according to some, or following interior to the labia minora to meet at the fourchette, according to others.
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. An article published in the Journal of Obstetrics and Gynecology in July 1992 states that the average width of the clitoral glans lies within the range of 2.5 – 4.5 mm (0.10-0.18 in), indicating that the average size is smaller than a pencil eraser. There is no identified correlation between the size of a clitoris and a woman's age, height, weight, use of oral contraceptives, or being post-menopausal. Those who have given birth tend to have slightly larger measurements.
Masters and Johnson were the first to determine that the clitoral structures surround and extend along the vagina, determining that all orgasms are of clitoral origin. More recently, Australian urologist Dr. Helen O'Connell, using MRI technology, 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. She asserts that this interconnected relationship is the physiological explanation for the conjectured G-spot and experience of vaginal orgasm taking into account the stimulation of the internal parts of the clitoris during vaginal penetration. Some individuals who experience orgasm from both direct clitoral stimulation of the glans and vaginal access to the internal bodies may distinguish between them in terms of both the physical and general sensations associated with each.
During sexual arousal and during orgasm, the clitoris and the whole of the genitalia engorge and change color as these erectile tissues fill with blood, and the individual experiences vaginal contractions. Masters and Johnson documented the sexual response cycle, which has four phases and is still the clinically accepted definition of the human orgasm. More recent research has determined that some can experience a sustained intense orgasm through stimulation of the clitoris and remain in the orgasmic phase for much longer than the original studies indicated, evidenced by genital engorgement, color changes, and vaginal contractions.
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. Caspar Bartholin, a 17th century Danish anatomist, dismissed both claims, arguing that the clitoris had been widely known to medical science since the 2nd century. Indeed, Hippocrates used the term columella (little pillar). Avicenna named the clitoris the albatra or virga (rod). Albucasis, an Arabic medical authority, named it tentigo (tension). It was also known to the Romans, who named it (vulgar slang) landica.
This cycle of suppression and discovery continued, notably in the work of De Graaf (Tractatus de Virorum Organis Generationi Inservientibus, De Mulierum Organis Generationi Inservientibus Tractatus Novus) in the 17th century and Kobelt (Die männlichen und weiblichen Wollustorgane des Menschen und einiger Säugetiere) in the 19th. De Graaf criticised Columbo's claims for this. (Harvey, Laqueur).
The full extent of the clitoris was alluded to by Masters and Johnson in 1966, but in such a muddled fashion that the significance of their description became obscured. That same year, feminist psychiatrist Mary Jane Sherfey published an article on female sexuality that described in detail the extensive nature of the internal anatomy of the clitoris and in 1981, the Federation of Feminist Women's Health Clinics (FFWHC) continued this process with anatomically precise illustrations. Today, MRI complements these efforts, as it is both a live and multiplanar method of examination.
The external part of the clitoris may be partially or totally removed during female genital cutting, also known as a clitoridectomy, female circumcision, or female genital mutilation (FGM); this may be a voluntary or involuntary procedure. The topic is highly controversial with many countries condemning the traditions that give rise to involuntary procedures, and with some countries outlawing even voluntary procedures. Amnesty International estimates that over 2 million involuntary female circumcisions are being performed every year, mainly in African countries.
In various cultures, the clitoris is sometimes pierced directly. In U.S. body modification culture, it is actually extremely rare for the clitoral shaft itself to be pierced, as of the already few people who desire the piercing, only a small percentage are anatomically suited for it; furthermore, most piercing artists are reluctant to attempt such a delicate procedure. Some styles, such as the Isabella, do 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 shaft piercings. Additionally, what is (erroneously) referred to as a "clit piercing" is almost always the much more common (and much less complicated) clitoral hood piercing.
Enlargement may be intentional or unintentional. Those taking hormones and/or other medications as part of female-to-male transition usually experience dramatic clitoral growth; individual desires (and the difficulties of surgical phalloplasty) often result in the retention of the original genitalia, the enlarged clitoris analogous to a penis as part of the transition. However, the clitoris never completely adapts to the masculinization of its owner and will never be able to ejaculate or urinate and is small in comparison to the genitalia of a natural born male. On the other hand, use of anabolic steroids by bodybuilders and other athletes can result in significant enlargement of the clitoris in concert with other masculinizing effects on their bodies. Temporary engorgement results from suction pumping, practiced to enhance sexual pleasure or for aesthetic purposes.
Male-to-female transsexual individuals who undergo sex reassignment surgery (male-to-female) (SRS) may choose to have their surgeon design a clitoris, using their existing genital tissue. The new clitoris may be referred to as a neoclitoris.