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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.

In different animals

Vertebrates

Mammals

[REDACTED] Media related to Mammal penis at Wikimedia Commons

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:

• Roots (crura): these begin at the caudal border of the pelvic ischial arch.
• Body: the part of the penis extending from the roots.
• Glans: the free end of the penis.

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.

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.

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.

Canidae

Canids, including dogs, have a bulbus glandis at the base of their penis. 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.

Felidae

Cats have barbed penises, with about 120–150 one millimeter long backwards-pointing spines. Upon withdrawal of the penis, the spines rake the walls of the female's vagina, which is a trigger for ovulation.

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.

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

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.

Marsupials

Most marsupials, except for the two largest species of kangaroos, have a bifurcated penis, separated into two columns, so that the penis has two ends corresponding to the females' two vaginas. Neither marsupials nor monotremes possess a baculum.

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.

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.

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.

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), Anatidae (ducks, geese and swans), and a very few other species (such as flamingoes). 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. 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.

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

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.

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, 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."

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 images, pictorial or carved, of the penis.

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

• Baculum
• Bulbus glandis
• Buried Penis
• Castration complex
• Diphallia
• Dildo
• Erogenous zone
• Human penis
• Koteka
• Micropenis
• Penis enlargement
• Penis envy
• Penis Plant
• Penis removal
• Penis size
• Phallic architecture
• Phallus
• Preputial mucosa
• Preputioplasty
• Pseudo-penis
• Pubic hair
• Stamen
• Stunt cock
• Testicle
• Vulva

References

1. Reece, William O. (2009). Functional Anatomy and Physiology of Domestic Animals. John Wiley and Sons. ISBN 978-0-8138-1451-3.
2. ^ Sarkar, A. (2003). Sexual Behaviour In Animals. Discovery Publishing House. ISBN 978-81-7141-746-9.
3. "Functional Anatomy and Physiology of Domestic Animals - William O. Reece - Google Boeken". Books.google.com. Retrieved 2012-12-02.
4. "Modern Livestock and Poultry Production - James R. Gillespie, Frank B. Flanders - Google Boeken". Books.google.com. Retrieved 2012-12-02.
5. Aronson, L. R.; Cooper, M. L. (1967). "Penile spines of the domestic cat: their endocrine-behavior relations" (PDF). Anat. Rec. 157 (1): 71–8. doi:10.1002/ar.1091570111. PMID 6030760.
6. Feldhamer, George A.; Thompson, Bruce C.; Chapman, Joseph A. (2003). Wild mammals of North America : biology, management, and conservation (2nd ed. ed.). Baltimore, Md.: Johns Hopkins University Press. p. 432. ISBN 9780801874161. {{cite book}}: |edition= has extra text (help)
7. ^ "The Largest Penis in the World – Both for humans and animals, size does matter! – Softpedia". News.softpedia.com. 2007-01-05. Retrieved 2011-05-28.
8. "Dolphin Chronicles - Carol J. Howard - Google Books". Books.google.com. Retrieved 2012-11-22.
9. "The Dusky Dolphin: Master Acrobat Off Different Shores - Bernd G. Würsig, Bernd Wursig, Melany Wursig - Google Books". Books.google.com. Retrieved 2012-11-22.
10. "Conservation Endangered Spe: An Interdisciplinary Approach - Edward F. Gibbons, Jr., Barbara Susan Durrant, Jack Demarest - Google Books". Books.google.com. Retrieved 2012-11-22.
11. Anna King (2001). "Discoveries about Marsupial Reproduction". Iowa State University Biology Dept. Retrieved 2012-11-22. {{cite web}}: Unknown parameter |webpage= ignored (help)
12. "Walker's Mammals of the World - Ronald M. Nowak - Google Boeken". Books.google.com. Retrieved 2012-12-02.
13. "Reproductive Physiology of Marsupials - Hugh Tyndale-Biscoe, Marilyn Renfree - Google Boeken". Books.google.com. 1987-01-30. Retrieved 2012-12-02.
14. "Predators With Pouches: The Biology of Carnivorous Marsupials - Menna Jones, Chris R. Dickman, Mike Archer, Michael Archer - Google Boeken". Books.google.com. 2003-04-30. Retrieved 2012-12-02.
15. "Chasing Kangaroos: A Continent, a Scientist, and a Search for the World's ... - Tim Flannery - Google Books". Books.google.com. Retrieved 2012-12-02.
16. "Walker's Mammals of the World - Ronald M. Nowak - Google Boeken". Books.google.com. Retrieved 2012-12-02.
17. Human penis is larger than that of any other primate. Darwin's legacy: scenarios in human evolution, p. 121. S.T. Parker, K.E. Jaffe.
18. Shultz, N. (2007-10-26). "Exhibitionist spiny anteater reveals bizarre penis". New Scientist website. Retrieved 2006-10-27. {{cite web}}: External link in |work= (help)
19. Attention: This template ({{cite doi}}) is deprecated. To cite the publication identified by doi:10.1111/j.1467-8721.2007.00473.x, please use {{cite journal}} (if it was published in a bona fide academic journal, otherwise {{cite report}} with |doi=10.1111/j.1467-8721.2007.00473.x instead.
20. Lutz, Dick (2005), Tuatara: A Living Fossil, Salem, Oregon: DIMI PRESS, ISBN 0-931625-43-2
21. Simpson, John; Weiner, Edmund, eds. (1989). "yard, n.". Oxford English Dictionary (2nd ed.). Oxford University Press. Online edition, print version ISBN 978-0-19-861186-8, CD-ROM ISBN 978-0-19-861016-8.
22. Simpson, John, ed. (2005). "penis, n.". Oxford English Dictionary (Draft revision September 2005 ed.). Oxford University Press. Online edition. (1989 second edition: ISBN 978-0-19-861186-8, CD-ROM ISBN 978-0-19-861016-8)
23. "Online Etymology Dictionary". Etymonline.com. Retrieved 2011-05-28.

External links

[REDACTED] Media related to Penis at Wikimedia Commons

• Kinsey Institute on the penis

Topics related to Penis

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• Penis
• Mammal male reproductive system