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Penis

The penis (plural penises or penes) or phallus is the male copulatory organ, and, in mammals, the male organ of urinary excretion. It is homologous to the female clitoris, as it develops from the same embryonic structure. The male sexual organs comprise both the penis and the testes. The penis is capable of erection for use in sexual intercourse.

Table of contents
1 Animal penises
2 The human penis
3 Disorders affecting the penis
4 Body modification
5 Penis size myths and legends

Animal penises

Most marsupials, except for the two largest species of kangaroos, have a bifurcated penis. That is, it separates into two separate columns, and so the penis terminates in two ends. The dolphins have independent control over their penises, so they use it as an appendage to feel the bottom with. The barnacle has the longest penis for its own length: up to twenty times the length of the animal.

The human penis

The human penis differs from some other mammalian penises by lacking an erectile bone, instead relying entirely on engorgement with blood to reach its erect state, lacking the ability to be withdrawn into the groin, and being larger than average in proportion to body mass.

Structure

The human penis is built of three columns of erectile tissue:

The end of corpus spongiosum is enlarged and cone-shaped and forms the glans penis. The glans supports the foreskin or prepuce, a loose fold of skin that can retract to expose the glans. It aids in sexual insertion, keeps the glans moist and provides a gliding action which is said to increase sexual pleasure for the man and his partner as well. For various culturual, religious, and more rarely medical reasons, the foreskin is sometimes partly or completely removed; this is called circumcision. Removal of the same tissue in females is considered a genital mutilation and is outlawed in many countries. The area on the underside of the penis, where the foreskin attaches, is called the frenum (or frenulum). The inner portion of the foreskin near the sulcus is a highly innervated area known as the ridged band. Removal of the foreskin by circumcision also usually removes the ridged band and injures or removes the frenulum.

The urethra, which is the last part of the urinary tract, traverses the corpus spongiosum and its end lies on the tip of the glans penis. It is both a passage for urine and for the ejaculation of semen. Sperm is produced in the testes and stored in the attached epididymis. During ejaculation, sperm are propelled up the vas deferens, two ducts that pass over and behind the bladder. Fluids are added by the seminal vesicles and the vas deferens turns into the ejaculatory ducts which join the urethra inside the prostate gland. The prostate as well as the bulbourethral glands add further secretions, and the semen is expelled through the penis.


Male internal sexual anatomy

Erection


A semierect penis

Erection is a stiffening and hardening of the penis which occurs in the sexually aroused male. Erection enables sexual intercourse, though it is not essential, and some other sexual activities.

Size

In comparison to body size, the human male penis is among the largest of the primates. From polling, the average human male penis is 5 1/2 inches (14 cm) in length when fully engorged with blood during arousal, though this varies quite a bit. The size of a flaccid human penis has an even greater variation in both length and width that often does not predict the size of a fully aroused member. For example, a man with a relatively small flaccid penis may have an above average length penis when fully aroused. The opposite is also true.

Disorders affecting the penis

In Peyronie's disease, anomalous scar tissue grows in the soft tissue of the penis.

Pudendal nerve entrapment is a condition characterized by pain on sitting and loss of penis (or clitoris) sensation and orgasm. In fact, sometimes there is a total loss of sensation and orgasm. The pudendal nerve can be damaged by narrow hard cycle seats and accidents. In females it commonly occurs as a result of childbirth. It is treated in France (the leaders in this area), America and Egypt.

Penile fracture can occur if the erect penis is bent excessively.

Developmental disorders of the penis

Hypospadias is a developmental disorder of the penis, where the meatus is positioned wrongly at birth. It is usually corrected by surgery.

A micropenis is a very small penis caused by developmental problems.

Psychological disorders related to the penis

Body modification

The most common form of penile body modification is the common but controversial practice of circumcision.

Less commonly, the penis is sometimes pierced and modified by other body art. Piercings of the penis include the Prince Albert piercing, the Apadravya piercing, the Ampallang piercing, the dido piercing, the frenum piercing and others.

Other physical modifications to the penis are also performed by some people, although they are considered very extreme. Apart from a penectomy, perhaps the most radical of these is the subincision, in which the glans penis is bifurcated to look similar to that of the kangaroo. This modification was originally done among Australian Aborigines, although it is now done by some in the U.S. and Europe.

A small number of men who are circumcised attempt to restore their foreskin through various means, including surgical. This is called foreskin restoration.

Penis size myths and legends

(see also the more detailed article on penis size)

Many people are highly concerned with penis size. Some men seek penis enlargement, as they perceive that their penis is "too small". Studies have shown that most men seeking penis enlargement have normal-sized penises.

Many cultures have a persistent urban legend that the penis size of some minority groups is larger than the norm. In the United States, the minority group chosen are African-Americans. This appears not to be supported by anything other than anecdote. Fanon covers this subject in some detail in "Black Skin, White Masks", and tends to agree that this is a myth (which he backs up with statistics).

The only reliable penis-size studies commonly quoted in the literature are the Kinsey study, the UCSF study, and an Italian study, none of which even attempted to correlate with race. There is an ongoing government study in India as well (commissioned with the goal of helping reduce the high condom failure rate there), but it too is unlikely to answer the question. There have been many other studies and claims of varying rigor--for example, the LifeStyles condoms study, but they are generally flawed by selection bias.

See also: impotence, lingam, penis envy, priapism, circumcision, sexual intercourse, Sexual slang, and the movie Percy.