for: phallus

The penis (plural penises, penes) is an external sexual organ of certain biologically male organisms, in both vertebrates and invertebrates.

The penis is a reproductive organ, technically an intromittent organ, and for placental mammals, additionally serves as the external organ of urination. The penis is generally found on mammals and reptiles.

Etymology

The word "penis" is taken from the Latin word for "tail." Some derive that from Indo-European *pesnis, and the Greek word πεος = "penis" from Indo-European *pesos. Prior to the adoption of the Latin word in English the penis was referred to as a "yard". The Oxford English Dictionary cites an example of the word yard used in this sense from 1379, and notes that in his Physical Dictionary of 1684, Steven Blankaart defined the word penis as "the Yard, made up of two nervous Bodies, the Channel, Nut, Skin, and Fore-skin, etc." (1989 second edition: ISBN 978-0-19-861186-8, CD-ROM ISBN 978-0-19-861016-8)

The Latin word "phallus" (from Greek φαλλος) is sometimes used to describe the penis, although "phallus" originally was used to describe images, pictorial or carved, of the penis.

The adjectival form of the word penis is penile. This adjective is commonly used in describing the male copulatory organ's various accessory structures which are commonly found in many kinds of invertebrate animals.

Slang

As with nearly any aspect of the human body that is involved in sexual or excretory functions, the word penis is considered inherently funny from a juvenile perspective, and there are many slang words for the penis, such as "cock", "dick", "shlong", or "willy". Many of these are noted in the bathroom humor article.

"Penii" is sometimes facetiously or mistakenly used as a plural form of "penis" instead of "penes" or "penises," its correct forms.

Structure

The enlarged and bulbous-shaped end of the corpus spongiosum forms the glans penis, which supports the foreskin or prepuce, a loose fold of skin that in adults can retract to expose the glans. The area on the underside of the penis, where the foreskin is attached, is called the frenum (or frenulum).

The raphe is the visible ridge between the lateral halves of the penis, found on the ventral or underside of the penis, running from the meatus (opening of the urethra) across the scrotum to the perineum (area between scrotum and anus).

The human penis differs from those of most other mammals, as it has no baculum, or erectile bone, and instead relies entirely on engorgement with blood to reach its erect state. It cannot be withdrawn into the groin, and it is larger than average in the animal kingdom in proportion to body mass.