Penis

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Penises of minke whales on display at the Icelandic Phallological Museum

Penis (plural penises or penes) is a general term for the organs with which male and hermaphrodite animals introduce sperm into receptive females during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males do not bear a penis in every animal species, and in those species in which the male does bear a so-called penis, the penes in the various species are not necessarily homologous. For example, the penis of a mammal is at most analogous to the penis of a male insect or barnacle.

The term penis applies to many reproductive intromittent organs, but not to all; for example the intromittent organ of most cephalopoda is the hectocotylus, a specialised arm, and male spiders use their pedipalps.

In most species of animals in which there is an organ that might reasonably be described as a penis, it has no major function other than intromission, or at least conveying the sperm to the female, but in the placental mammals the penis bears the distal part of the urethra, which discharges both urine during urination and semen during copulation as the occasion requires. The Blue Whale has the largest penis of any organism on the planet, typically measuring 8–10 feet.

Contents

In different animals

Mammals

As with any other bodily attribute, the length and girth of the penis can be highly variable between individuals of the same species. In many animals, especially mammals, the size of a flaccid penis is smaller than its erect size.

A bone called the baculum or os penis is present in most mammals but absent in humans and horses.

In mammals the penis is divided into three parts:[1]

The internal structures of the penis consist mainly of cavernous, erectile tissue, which is a collection of blood sinusoids separated by sheets of connective tissue (trabeculae). Some mammals have a lot of erectile tissue relative to connective tissue, for example horses. Because of this a horse's penis can enlarge more than a bull's penis. The urethra is on the ventral side of the body of the penis.

Elephants

An adult elephant has the largest penis of any land animal at 6 feet (1.8 m) on average.[2] An elephant's penis can reach a length of 100 cm (39 in) and a diameter of 16 cm (6 in) at the base. It is S-shaped when fully erect and has a Y-shaped orifice.[3] During musth, a male elephant may urinate with the penis still in the sheath, which causes the urine to spray on the hind legs.[4]

Tapiridae

Tapirs have exceptionally long penises relative to their body size.[5][6][further explanation needed]

Deer

A stag's penis forms an S-shaped curve when it is not erect, and is retracted into its sheath by the retractor penis muscle.[7] Red deer stags often have erect penises during combat.[8] A sambar stag will mark itself by spraying urine directly in the face with a highly mobile penis, which is often erect during its rutting activities..[9]

Horse

Stallions have a vascular penis. When non-erect, it is quite flaccid and contained within the prepuce (foreskin, or sheath). The retractor penis muscle is relatively underdeveloped. Erection and protrusion take place gradually, by the increasing tumescence of the erectile vascular tissue in the corpus cavernosum penis.[10]

Bulls

Bulls have a fibro-elastic penis. Given the small amount of erectile tissue, there is little enlargement after erection. The penis is quite rigid when non-erect, and becomes even more rigid during erection. Protrusion is not affected much by erection, but more by relaxation of the retractor penis muscle and straightening of the sigmoid flexure.[10][11][12] Bulls are occasionally affected by a condition known as "corkscrew penis"[further explanation needed].[13][14]

Carnivora

All members of Carnivora (except hyenas) have a baculum.[15]

Caniformia

In the Canoidea, the penis is highly specialized.[16][further explanation needed]

Canidae

Canids, including wolves[17][18][19][20] and dogs, have a bulbus glandis at the base of their penis. The penis sometimes emerges from the sheath during sexual arousal.[21] During coitus the bulbus glandis swells up and results in a 'tie' (the male and female dogs being tied together). Muscles in the vagina of the female assist the retention by contracting.[citation needed] Male dogs have a conspicuous penis sheath.[22]

Felidae

Cats have barbed penises, with about 120–150 one millimeter long backwards-pointing spines.[23] Upon withdrawal of the penis, the spines rake the walls of the female's vagina, which is a trigger for ovulation. Male felids usually urinate backwards by curving the tip of the glans penis backward.[24][16]

Fossa

Cetaceans

Whales

The penis on a right whale can be up to 2.7 m (8.9 ft) – the testes, at up to 2 m (6.6 ft) in length, 78 cm (2.56 ft) in diameter, and weighing up to 525 lb (238 kg), are also by far the largest of any animal on Earth.[25]

Accurate measurements of the blue whale are difficult to take because the whale's erect length can only be observed during mating.[26]

Dolphins

Dolphins' reproductive organs are located on the underside of the body. Males have two slits, one concealing the penis and one further behind for the anus.[27][28][29]

Marsupials

Most marsupials, except for the two largest species of kangaroos[clarify], have a bifurcated penis, separated into two columns, so that the penis has two ends corresponding to the females' two vaginas.[30][31][32][33][34] Neither marsupials nor monotremes possess a baculum.[35] When not erect, it is retracted into the body in an S-shaped curve.[32] The shape of the glans varies among species.[32][36][37][38][further explanation needed]

Other mammals

Bulls, rams and boars have an S-shaped penis with a sigmoid flexure which straightens out during erection.

As a general rule, a mammal's penis is proportional to its body size, but this varies greatly between species – even between closely related ones. For example, an adult gorilla's erect penis is about 4 cm (1.5 in) in length; an adult chimpanzee, significantly smaller (in body size) than a gorilla, has a penis size about double that of the gorilla. In comparison, the human penis is larger than that of any other primate, both in proportion to body size and in absolute terms.[39]

In the realm of absolute size, the smallest vertebrate penis belongs to the common shrew (5 mm or 0.2 inches).

Echidnas have a four-headed penis, but only two of the heads are used during mating. The other two heads "shut down" and do not grow in size. The heads used are swapped each time the mammal has sex.[40]

It has been postulated that the shape of the human penis may have been selected by sperm competition. The shape could have favored displacement of seminal fluids implanted within the female reproductive tract by rival males: the thrusting action which occurs during sexual intercourse can mechanically remove seminal fluid out of the cervix area from a previous mating.[41]

Birds

Most male birds (e.g., roosters and turkeys) have a cloaca (also present on the female), but not a penis. Among bird species with a penis are paleognathes (tinamous and ratites),[42] Anatidae (ducks, geese and swans),[17] and a very few other species (such as flamingoes[citation needed], chickens,[43] and ostriches[43][44]). A bird penis is different in structure from mammal penises, being an erectile expansion of the cloacal wall and being erected by lymph, not blood.[43] It is usually partially feathered and in some species features spines and brush-like filaments, and in flaccid state curls up inside the cloaca. The Argentine Blue-bill has the largest penis in relation to body size of all vertebrates; while usually about half the body size (20 cm), a specimen with a penis 42.5 cm long is documented.

Other vertebrates

Male turtles and crocodiles have a penis, while male specimens of the reptile order Squamata have two paired organs called hemipenes. Tuataras must use their cloacae for reproduction.[45]

In some fishes, the gonopodium, andropodium, and claspers are intromittent organs (to introduce sperm into the female) developed from modified fins.

The spine-covered penis of Callosobruchus analis, a Bean weevil.

Invertebrates

The record for the largest penis to body size ratio is held by the barnacle. The barnacle's penis can grow to up to forty times its own body length. This enables them to reach the nearest female.[26]

In male insects, the structure analogous to a penis is known as aedeagus. The male copulatory organ of various lower invertebrate animals is often called the cirrus.

A number of invertebrate species have independently evolved the mating technique of traumatic insemination where the penis penetrates the female's abdomen and deposits sperm in the wound it produces. This has been most fully studied in bedbugs.

Etymology

The word "penis" is taken from the Latin word for "tail." Some derive that from Indo-European *pesnis, and the Greek word πέος = "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,[46] 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."[47]

As with nearly any aspect of the body involved in sexual or excretory functions, the penis is the subject of many slang words and euphemisms for it, a particularly common and enduring one being "cock". See WikiSaurus:penis for a list of alternative words for penis.

The Latin word "phallus" (from Greek φαλλος) is sometimes used to describe the penis, although "phallus" originally was used to describe representations, pictorial or carved, of the penis.[48]

Pizzle, an archaic English word for penis, of Low German or Dutch origin, is now used to denote the penis of a non-human animal.

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

See also

References

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External links

Media related to Penis at Wikimedia Commons