A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or

hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...

s) during

copulation Sexual intercourse (or coitus or copulation) is a sexual activity typically involving the insertion and thrusting of the penis into the vagina for sexual pleasure or reproduction.Sexual intercourse most commonly means penile–vaginal penetrat ...

. 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 penises in the various species are not necessarily

homologous Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor *Sequence homology, biological homology between DNA, RNA, or protein sequences * Homologous chrom ...

. The term ''penis'' applies to many

intromittent organ An intromittent organ is any external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most non-mammalian aquatic species fertilize their eggs e ...

s, but not to all. As an example, the intromittent organ of most

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

a is the

hectocotylus A hectocotylus (plural: ''hectocotyli'') is one of the arms of male cephalopods that is specialized to store and transfer spermatophores to the female. Structurally, hectocotyli are muscular hydrostats. Depending on the species, the male may use i ...

, a specialized arm, and male spiders use their pedipalps. Even within the Vertebrata there are morphological variants with specific terminology, such as

hemipenes A hemipenis (plural hemipenes) is one of a pair of intromittent organs of male squamata, squamates (snakes, lizards and amphisbaenia, worm lizards). Hemipenes are usually held inverted within the body, and are everted for reproduction via erecti ...

. 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 Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

part of the urethra, which discharges both urine during urination and semen during copulation.

Vertebrates

Birds

Mallard with visible pseudo-penis (cropped)

Most male birds (e.g., roosters and turkeys) have a

cloaca In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...

(also present on the female), but not a penis. Among bird species with a penis are paleognathes ( tinamous and ratites) and Anatidae (ducks, geese and swans). 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

. While most male birds have no external genitalia, male waterfowl ( Anatidae) have a phallus. Most birds mate with the males balancing on top of the females and touching cloacas in a "cloacal kiss"; this makes forceful insemination very difficult. The phallus that male waterfowl have evolved everts out of their bodies (in a clockwise coil) and aids in inseminating females without their cooperation.Brennan, P. L. R. et al. Coevolution of male and female genital morphology in waterfowl. ''PLoS ONE'' 2, e418 (2007). The male waterfowl evolution of a phallus to forcefully copulate with females has led to counteradaptations in females in the form of vaginal structures called dead end sacs and clockwise coils. These structures make it harder for males to achieve intromission. The clockwise coils are significant because the male phallus everts out of their body in a counter-clockwise spiral; therefore, a clockwise vaginal structure would impede forceful copulation. Studies have shown that the longer a male's phallus is, the more elaborate the vaginal structures were. Duck Reproduction

The

lake duck The lake duck (''Oxyura vittata'') is a small, South American stiff-tailed duck. It is also called the Argentine blue-bill, Argentine blue-billed duck, Argentine lake duck, or Argentine ruddy duck. Description The lake duck grows to . Females ...

is notable for possessing, in relation to body length, the longest penis of all vertebrates; the penis, which is typically coiled up in flaccid state, can reach about the same length as the animal himself when fully erect, but is more commonly about half the bird's length. It is theorized that the remarkable size of their spiny penises with bristled tips may have evolved in response to competitive pressure in these highly promiscuous birds, removing sperm from previous matings in the manner of a bottle brush. The lake duck has a corkscrew shaped penis. Male and female

emu The emu () (''Dromaius novaehollandiae'') is the second-tallest living bird after its ratite relative the ostrich. It is endemic to Australia where it is the largest native bird and the only extant member of the genus ''Dromaius''. The emu' ...

s are similar in appearance,Eastman, p. 23. although the male's penis can become visible when it defecates.Coddington and Cockburn, p. 366. The male tinamou has a corkscrew shaped penis, similar to those of the ratites and to the hemipenis of some reptiles. Females have a small phallic organ in the cloaca which becomes larger during the breeding season.

Mammals

As with any other bodily attribute, the length and girth of the penis can be highly variable between mammals of different species. In many mammals, the size of a flaccid penis is smaller than its erect size. A bone called the

baculum The baculum (also penis bone, penile bone, or ''os penis'', ''os genitale'' or ''os priapi'') is a bone found in the penis of many placental mammals. It is absent from the human penis, but present in the penises of some primates, such as the ...

or ''os penis'' is present in most mammals but absent in humans, cattle and horses. In mammals the penis is divided into three parts: * Roots ( crura): these begin at the

caudal Caudal may refer to: Anatomy * Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism * Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into the ...

border of the pelvic ischial arch. *

Body Body may refer to: In science * Physical body, an object in physics that represents a large amount, has mass or takes up space * Body (biology), the physical material of an organism * Body plan, the physical features shared by a group of anima ...

: 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 Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

(trabeculae). Some mammals have a lot of erectile tissue relative to connective tissue, for example horses. Because of this a

horse's penis A stallion is a male horse that has not been gelded (castrated). Stallions follow the conformation and phenotype of their breed, but within that standard, the presence of hormones such as testosterone may give stallions a thicker, "cresty" neck ...

can enlarge more than a

bull's penis A bull is an intact (i.e., not castrated) adult male of the species ''Bos taurus'' (cattle). More muscular and aggressive than the females of the same species (i.e., cows), bulls have long been an important symbol in many religions, includin ...

. The urethra is on the ventral side of the body of the penis. As a general rule, a mammal's penis is proportional to its body size, but this varies greatly between specieseven between closely related ones. For example, an adult gorilla's erect penis is about in length; an adult

chimpanzee The chimpanzee (''Pan troglodytes''), also known as simply the chimp, is a species of great ape native to the forest and savannah of tropical Africa. It has four confirmed subspecies and a fifth proposed subspecies. When its close relative th ...

, 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.

Artiodactyls

The penises of even-toed ungulates are curved in an S-shape when not erect. In bulls,

rams In engineering, RAMS (reliability, availability, maintainability and safety)boars, the sigmoid flexure of the penis straightens out during erection. When mating, the tip of a male pronghorn's penis is often the first part to touch the female pronghorn. The pronghorn's penis is about long, and is shaped like an ice pick. The front of a pronghorn's glans penis is relatively flat, while the back is relatively thick. The male pronghorn usually

ejaculates Ejaculation is the discharge of semen (the ''ejaculate''; normally containing sperm) from the male reproductory tract as a result of an orgasm. It is the final stage and natural objective of male sexual stimulation, and an essential component ...

immediately after intromission. The penis of a dromedary camel is covered by a triangular penile sheath opening backwards, and is about long. The camelmen often aid the male to enter his penis into the female's vulva, though the male is considered able to do it on his own. Copulation time ranges from 7 to 35 minutes, averaging 11–15 minutes. 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 The sigmoid colon (or pelvic colon) is the part of the large intestine that is closest to the rectum and anus. It forms a loop that averages about in length. The loop is typically shaped like a Greek letter sigma (ς) or Latin letter S (thus ''s ...

. The male genitalia of mouse deer are similar to those of pigs. A boar's penis, which rotates rhythmically during copulation, is about long, and ejaculates about a pint of semen. Wild boars have a roughly egg-sized sack near the opening of the penis, which collects urine and emits a sharp odour. The purpose of this is not fully understood.Heptner, V. G.; Nasimovich, A. A.; Bannikov, A. G.; Hoffman, R. S. (1988
''Mammals of the Soviet Union''
Volume I, Washington, D.C. : Smithsonian Institution Libraries and National Science Foundation, pp. 19-82

=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. Some deer species spray urine on their bodies by urinating from an erect penis. One type of scent-marking behavior in elk is known as "thrash-urination, which typically involves palpitation of the erect penis. A male elk's urethra points upward so that urine is sprayed almost at a right angle to the penis. A sambar stag will mark himself by

spraying urine Urination, also known as micturition, is the release of urine from the urinary bladder through the urethra to the outside of the body. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, uresis, ...

directly in the face with a highly mobile penis, which is often erect during its rutting activities.''Deer of the world: their evolution, behaviour, and ecology.'' Valerius Geist. Stackpole Books. 1998. Pg. 73-77. Red deer stags often have erect penises during combat.

Cetaceans

Cetaceans' reproductive organs are located inside the body. Male

cetaceans Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel them ...

(whales, dolphins, and porpoises) have two slits, the genital groove concealing the penis and one further behind for the

anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, d ...

. Cetaceans have fibroelastic penises, similar to those of Artiodactyla. The tapering tip of the cetacean penis is called the ''pars intrapraeputialis'' or ''terminal cone''. The blue whale has the largest penis of any organism on the planet, typically measuring . Accurate measurements are difficult to take because its erect length can only be observed during mating, which occurs underwater. The penis on a

right whale Right whales are three species of large baleen whales of the genus ''Eubalaena'': the North Atlantic right whale (''E. glacialis''), the North Pacific right whale (''E. japonica'') and the Southern right whale (''E. australis''). They are clas ...

can be up to – the testes, at up to in length, in diameter, and weighing up to , are also by far the largest of any animal on Earth. On at least one occasion, a dolphin towed bathers through the water by hooking his erect penis around them. Between male bottlenose dolphins,

homosexual behaviour Homosexuality is romantic attraction, sexual attraction, or sexual behavior between members of the same sex or gender. As a sexual orientation, homosexuality is "an enduring pattern of emotional, romantic, and/or sexual attractions" to peop ...

includes rubbing of genitals against each other, which sometimes leads to the males swimming belly to belly, inserting the penis in the other's genital slit and sometimes anus.

Perissodactyls

Stallion A stallion is a male horse that has not been gelded (castrated). Stallions follow the conformation and phenotype of their breed, but within that standard, the presence of hormones such as testosterone may give stallions a thicker, "cresty" nec ...

s (male horses) have a vascular penis. When non-erect, it is quite flaccid and contained within the

prepuce Prepuce , or as an adjective, preputial , refers to two homologous structures of male and female genitals: *Clitoral hood, skin surrounding and protecting the head of the clitoris *Foreskin, skin surrounding and protecting the head of the penis in ...

(foreskin, or sheath). Tapirs have exceptionally long penises relative to their body size. The glans of the Malayan tapir resembles a mushroom, and is similar to the glans of the horse. The penis of the Sumatran rhinoceros contains two lateral lobes and a structure called the ''processus glandis''.

Carnivores

All members of

Carnivora Carnivora is a Clade, monophyletic order of Placentalia, placental mammals consisting of the most recent common ancestor of all felidae, cat-like and canidae, dog-like animals, and all descendants of that ancestor. Members of this group are f ...

(except hyenas) have a baculum. Canine penises have a structure at the base called the

bulbus glandis The bulbus glandis (also called a bulb or knot) is an erectile tissue structure on the penis of canid mammals. During mating, immediately before ejaculation the tissues swell up to lock ('' tie'') the male's penis inside the female. The locking i ...

. During copulation, the spotted hyena inserts his penis through the female's pseudo-penis instead of directly through the vagina, which is blocked by the false scrotum and testes. Once the female retracts her clitoris, the male enters the female by sliding beneath her, an operation facilitated by the penis's upward angle. The pseudo-penis closely resembles the male hyena's penis, but can be distinguished from the male's genitalia by its greater thickness and more rounded glans. In male spotted hyenas, as well as females, the base of the glans is covered with penile spines.

Domestic cats The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of t ...

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. Lions also have barbed penises. Male felids urinate backwards by curving the tip of the glans penis backward. When male cheetahs urine-mark their territories, they stand one meter away from a tree or rock surface with the tail raised, pointing the penis either horizontally backward or 60° upward. The male

fossa Fossa may refer to: Animals * Fossa (animal), the common name of a carnivoran mammal of genus ''Cryptoprocta'' endemic to Madagascar * ''Fossa'', the Latin genus name of the Malagasy civet, a related but smaller mammal endemic to Madagascar Pla ...

has an unusually long penis and

(penis bone), reaching to between his

front leg A forelimb or front limb is one of the paired articulated appendages (limbs) attached on the cranial (anterior) end of a terrestrial tetrapod vertebrate's torso. With reference to quadrupeds, the term foreleg or front leg is often used instead. ...

s when erect with backwards-pointing spines along most of its length. The male fossa has scent glands near the penis, with the penile glands emitting a strong odor. The beech marten's penis is larger than the pine marten's, with the

bacula Bacula is an open-source, enterprise-level computer backup system for heterogeneous networks. It is designed to automate backup tasks that had often required intervention from a systems administrator or computer operator. Bacula supports Lin ...

of young beech martens often outsizing those of old pine martens. Raccoons have penis bones which bend at a 90 degree angle at the tip. The extrusibility of a raccoon's penis can be used to distinguish mature males from immature males. Male walruses possess the largest penis bones of any land mammal, both in absolute size and relative to body size. The adult male American mink's penis is long, and is covered by a

sheath Sheath pronounced as , may refer to: * Scabbard, a sheath for holding a sword, knife, or other large blade, as well as guns, such as rifles. * The outer covering of a cable * Condom, a kind of contraception * Debye sheath, a layer of a plasma in ...

. The

is well-developed, being triangular in cross section and curved at the tip.

Bats

Males of

Racey's pipistrelle bat ''Pipistrellus raceyi'', also known as Racey's pipistrelle, is a bat from Madagascar, in the genus ''Pipistrellus''. Although unidentified species of ''Pipistrellus'' had been previously reported from Madagascar since the 1990s, ''P. raceyi' ...

have a long, straight penis with a notch between the shaft and the narrow, egg-shaped glans penis. Near the top, the penis is haired, but the base is almost naked. In the

(penis bone), the shaft is long and narrow and slightly curved. The length of the penis and baculum distinguish ''P. raceyi'' from all comparably sized African and Malagasy vespertilionids. In males, penis length is and baculum length is . Copulation by male greater short-nosed fruit bats is dorsoventral and the females lick the shaft or the base of the male's penis, but not the glans which has already penetrated the vagina. While the females do this, the penis is not withdrawn and research has shown a positive relationship between length of the time that the penis is licked and the duration of copulation. Post copulation genital grooming has also been observed.

Rodents

The glans penis of the

marsh rice rat The marsh rice rat (''Oryzomys palustris'') is a semiaquatic North American rodent in the family Cricetidae. It usually occurs in wetland habitats, such as swamps and salt marshes. It is found mostly in the eastern and southern United States, fr ...

is long and robust, averaging long and broad, and the baculum (penis bone) is long. As is characteristic of

Sigmodontinae The rodent subfamily Sigmodontinae includes New World rats and mice, with at least 376 species. Many authorities include the Neotominae and Tylomyinae as part of a larger definition of Sigmodontinae. When those genera are included, the specie ...

, the marsh rice rat has a complex penis, with the distal (far) end of the baculum ending in three digits. The central digit is notably larger than those at the sides. The outer surface of the penis is mostly covered by small spines, but there is a broad band of nonspinous tissue. The papilla (nipple-like projection) on the dorsal (upper) side of the penis is covered with small spines, a character the marsh rice rat shares only with ''

Oligoryzomys ''Oligoryzomys'' is a genus of rodents in the tribe Oryzomyini of family Cricetidae. Many species are known as pygmy rice rats or colilargos.Musser and Carleton, 2005 The genus is found from Mexico to Tierra del Fuego and includes approximately 1 ...

'' and ''Oryzomys couesi'' among oryzomyines examined. On the urethral process, located in the crater at the end of the penis, a fleshy process (the subapical lobule) is present; it is absent in all other oryzomyines with studied penes except ''O. couesi'' and '' Holochilus brasiliensis''. The baculum is deeper than it is wide. In ''

Transandinomys talamancae ''Transandinomys talamancae'' is a rodent in the family Cricetidae that occurs from Costa Rica to southwestern Ecuador and northern Venezuela. Its habitat consists of lowland forests up to above sea level. With a body mass of , it is a medium-s ...

'', the outer surface of the penis is mostly covered by small spines, but there is a broad band of nonspinous tissue. Some features of the accessory glands in the male genital region vary among

oryzomyines Oryzomyini is a tribe (taxonomy), tribe of rodents in the subfamily Sigmodontinae of the family Cricetidae. It includes about 120 species in about thirty genera,Weksler et al., 2006, table 1 distributed from the eastern List of mammals of the Uni ...

. In ''Transandinomys talamancae'', a single pair of preputial glands is present at the penis. As is usual for sigmodontines, there are two pairs of ventral prostate glands and a single pair of

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

and dorsal prostate glands. Part of the end of the

vesicular gland The seminal vesicles (also called vesicular glands, or seminal glands) are a pair of two convoluted tubular glands that lie behind the urinary bladder of some Sexual reproduction#Male, male mammals. They secrete fluid that partly composes the se ...

is irregularly folded, not smooth as in most oryzomyines. In

Pseudoryzomys ''Pseudoryzomys simplex'', also known as the Brazilian false rice rat or false oryzomys, is a species of rodent in the family Cricetidae from south-central South America. It is found in lowland palm savanna and thorn scrub habitats. It is a me ...

, the

(penis bone) displays large protuberances at the sides. In the cartilaginous part of the baculum, the central digit is smaller than those at the sides. In

Drymoreomys ''Drymoreomys'' is a rodent genus in the tribe Oryzomyini that lives in the Atlantic Forest of Brazil. The single species, ''D. albimaculatus'', is known only from the states of São Paulo and Santa Catarina and was not named until 2011. I ...

, there are three digits at the tip of the penis, of which the central one is the largest. In '' Thomasomys ucucha'' the glans penis is rounded, short, and small and is superficially divided into left and right halves by a trough at the top and a ridge at the bottom. The glans penis of a male cape ground squirrel is large with a prominent baculum. Unlike other squirrel species,

red squirrel The red squirrel (''Sciurus vulgaris'') is a species of tree squirrel in the genus ''Sciurus'' common throughout Europe and Asia. The red squirrel is an arboreal, primarily herbivorous rodent. In Great Britain, Ireland, and in Italy numbers ...

s have long, thin, and narrow penises, without a prominent baculum.

Winkelmann's mouse Winkelmann's mouse (''Peromyscus winkelmanni'') is a species of rodent in the family Cricetidae found only in Mexico, and is named for John R. Winkelmann, who collected the first specimens. Description Rather larger than a house mouse, an adult ...

can easily be distinguished from its close relatives by the shape of its penis, which has a partially corrugated glans. The foreskin of a

capybara The capybaraAlso called capivara (in Brazil), capiguara (in Bolivia), chigüire, chigüiro, or fercho (in Colombia and Venezuela), carpincho (in Argentina, Paraguay and Uruguay) and ronsoco (in Peru). or greater capybara (''Hydrochoerus hydro ...

is attached to the anus in an unusual way, forming an anogenital invagination.

Primates

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 fluid Semen, also known as seminal fluid, is an organic bodily fluid created to contain spermatozoa. It is secreted by the gonads (sexual glands) and other sexual organs of male or hermaphroditic animals and can fertilize the female ovum. Semen i ...

s 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 The cervix or cervix uteri (Latin, 'neck of the uterus') is the lower part of the uterus (womb) in the human female reproductive system. The cervix is usually 2 to 3 cm long (~1 inch) and roughly cylindrical in shape, which changes during ...

area from a previous mating. The penile morphology of some types of strepsirrhine primates has provided information about their taxonomy. Male galago species possess very distinctive penile morphology that can be used to classify species. The northern greater galago penis is on average in length, with doubled headed or even tridentate spines pointing towards the body. They are less densely packed than in ''Otolemur crassicaudatus''. The penis of the

ring-tailed lemur The ring-tailed lemur (''Lemur catta'') is a large strepsirrhine primate and the most recognized lemur due to its long, black and white ringed tail. It belongs to Lemuridae, one of five lemur families, and is the only member of the ''Lemur'' ge ...

is nearly cylindrical in shape and is covered in small spines, as well as having two pairs of larger spines on both sides. The adult male of each vervet monkey species has a pale blue scrotum and a red penis, and male

proboscis monkey The proboscis monkey (''Nasalis larvatus'') or long-nosed monkey is an arboreal Old World monkey with an unusually large nose, a reddish-brown skin color and a long tail. It is endemic to the southeast Asian island of Borneo and is found mostly ...

s have a red penis with a black scrotum. Male

baboons Baboons are primates comprising the genus ''Papio'', one of the 23 genera of Old World monkeys. There are six species of baboon: the hamadryas baboon, the Guinea baboon, the olive baboon, the yellow baboon, the Kinda baboon and the chacma ba ...

and

squirrel monkeys Squirrel monkeys are New World monkeys of the genus ''Saimiri''. ''Saimiri'' is the only genus in the subfamily Saimirinae. The name of the genus is of Tupi origin (''sai-mirím'' or ''çai-mbirín'', with ''sai'' meaning 'monkey' and ''mirím'' ...

sometimes gesture with an erect penis as both a warning of impending danger and a threat to predators. In male squirrel monkeys, this gesture is used for social communication.

=Humans

The human penis is an external sex organ of male humans. It is a

reproductive The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are als ...

that additionally serves as the urinal duct. The main parts are the root of the penis (radix): It is the attached part, consisting of the bulb of penis in the middle and the

crus of penis For their anterior three-fourths the corpora cavernosa penis lie in intimate apposition with one another, but behind they diverge in the form of two tapering processes, known as the crura, which are firmly connected to the ischial rami. Traced f ...

, one on either side of the bulb; the body of the penis (corpus); and the

epithelium Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...

of the penis consists of the shaft skin, the foreskin, and the

preputial mucosa The preputial mucosa of the penis is the epithelium of the inside of the prepuce, or foreskin. To differentiate it from the cutaneous skin of the outside of the prepuce, it is sometimes referred to as the inner mucosa. It starts at the ridged band ...

on the inside of the foreskin and covering the glans penis. The human penis is made up of three columns of tissue: two corpora cavernosa lie next to each other on the dorsal side and one corpus spongiosum lies between them on the

ventral side Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

. The urethra, which is the last part of the urinary tract, traverses the corpus spongiosum, and its opening, known as the meatus , lies on the tip of the glans penis. It is a passage both for urine and for the ejaculation of semen. In males, the expulsion of urine from the body is done through the penis. The urethra drains the bladder through the prostate gland where it is joined by the

ejaculatory duct The ejaculatory ducts (''ductus ejaculatorii'') are paired structures in male anatomy. Each ejaculatory duct is formed by the union of the vas deferens with the duct of the seminal vesicle. They pass through the prostate, and open into the ureth ...

, and then onward to the penis. An erection is the stiffening and rising of the penis, which occurs during

sexual arousal Sexual arousal (also known as sexual excitement) describes the physiological and psychological responses in preparation for sexual intercourse or when exposed to sexual stimuli. A number of physiological responses occur in the body and mind as ...

, though it can also happen in non-sexual situations. Ejaculation is the ejecting of semen from the penis and is usually accompanied by orgasm. A series of muscular contractions delivers semen, containing male gametes known as sperm cells or spermatozoa, from the penis. The most common form of genital alteration is circumcision, the removal of part or all of the foreskin for various cultural, religious, and more rarely medical reasons. There is controversy surrounding circumcision. , a

systematic review A systematic review is a Literature review, scholarly synthesis of the evidence on a clearly presented topic using critical methods to identify, define and assess research on the topic. A systematic review extracts and interprets data from publ ...

of 15,521 men, who were measured by health professionals rather than themselves, concluded that the average length of an erect human penis is 13.12 cm (5.17 inches) long, while the average circumference of an erect human penis is 11.66 cm (4.59 inches).

Marsupials

Most marsupials, except for the two largest species of kangaroos and marsupial moles (assuming the latter are true marsupials), have a bifurcated penis, separated into two columns, so that the penis has two ends corresponding to the females' two vaginas.

Monotremes

Monotreme Monotremes () are prototherian mammals of the order Monotremata. They are one of the three groups of living mammals, along with placentals (Eutheria), and marsupials (Metatheria). Monotremes are typified by structural differences in their brain ...

s and marsupial moles are the only mammals in which the penis is located inside the cloaca. Male echidnas have a bilaterally symmetrical, rosette-like, four-headed penis. During mating, the heads on one side "shut down" and do not grow in size; the other two are used to release semen into the female's two-branched reproductive tract. The heads used are swapped each time the mammal copulates.Augee, Gooden and Musser, p. 81. When not in use, the penis is retracted inside a preputial sac in the cloaca. The male echidna's penis is long when erect, and its shaft is covered with penile spines. The penis is nearly a quarter of his body length when erect.

Others

The penis of the

bush hyrax The yellow-spotted rock hyrax or bush hyrax (''Heterohyrax brucei'') is a species of mammal in the family Procaviidae. It is found in Angola, Botswana, Burundi, the Democratic Republic of the Congo, southern Egypt, Eritrea, Ethiopia, Kenya, Ma ...

is complex and distinct from that of the other hyrax genera. It has a short, thin appendage within a cup-like glans penis and measures greater than when erect. Additionally, it has been observed that the bush hyrax also has a greater distance between the anus and preputial opening in comparison to other hyraxes. An adult elephant has the largest penis of any land animal. An elephant's penis can reach a length of and a diameter of at the base. It is S-shaped when fully erect and has a Y-shaped orifice. During musth, a male elephant may urinate with his penis still in the

, which causes the urine to spray on the hind legs.Sukumar, pp. 100–08. An elephant's penis is very mobile, being able to move independently of the male's pelvis, and the penis curves forward and upward prior to mounting another elephant. In giant anteaters, the (retracted) penis and testes are located internally between the rectum and urinary bladder. When the male armadillo ''

Chaetophractus villosus The big (or large) hairy armadillo (''Chaetophractus villosus'') is one of the largest and most numerous armadillos in South America. It lives from sea level to altitudes of up to 1,300 meters across the southern portion of South America, and c ...

'' is

sexually aroused Sexual arousal (also known as sexual excitement) describes the physiological and psychological responses in preparation for sexual intercourse or when exposed to sexual stimuli. A number of physiological responses occur in the body and mind ...

, species determination is easier. Its penis can be as long as , and usually remains completely withdrawn inside a skin receptacle. Scientists conducting studies on the ''C. villosus'' penis muscles revealed this species' very long penis exhibits variability. During its waking hours, it remains hidden beneath a skin receptacle, until it becomes erect and it projects outside in a

rostral Rostral may refer to: Anatomy * Rostral (anatomical term), situated toward the oral or nasal region * Rostral bone, in ceratopsian dinosaurs * Rostral organ, of certain fish * Rostral scale, in snakes and scaled reptiles Other uses * Rostral colu ...

direction.

Fish and reptiles

Male turtles and

crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to inclu ...

s have a penis, while male specimens of the reptile order Squamata have two paired organs called

. Tuataras must use their cloacae for reproduction. Due to evolutionary convergence, turtle and mammal penises have a similar structure. In some fish, the gonopodium,

andropodium Fins are distinctive anatomical features composed of bony spine (zoology), spines or Ray (fish fin anatomy), rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bon ...

, and claspers are intromittent organs (to introduce sperm into the female) developed from modified fins.

Invertebrates

Arthropods

The record for the largest penis size to body size ratio is held by the

barnacle A barnacle is a type of arthropod constituting the subclass Cirripedia in the subphylum Crustacea, and is hence related to crabs and lobsters. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in eros ...

. The barnacle's penis can grow to up to forty times its own body length. This enables them to reach the nearest female for fertilization. A number of invertebrate species have independently evolved the mating technique of traumatic insemination where the penis penetrates the female's abdomen, thereby creating a womb into which it deposits sperm. This has been most fully studied in

bed bug Bed bugs are insects from the genus ''Cimex'' that feed on blood, usually at night. Their bites can result in a number of health impacts including skin rashes, psychological effects, and allergic symptoms. Bed bug bites may lead to skin changes ...

s. Some millipedes have penises. In these species, the penis is simply one or two projections on underneath the third body segment that produce a spermatophore or sperm packet. The act of insemination, however, occurs through specialized legs called

gonopods Gonopods are specialized appendages of various arthropods used in reproduction or egg-laying. In males, they facilitate the transfer of sperm from male to female during mating, and thus are a type of intromittent organ. In crustaceans and milli ...

which collect the spermatophore and insert it into the female.

Insects

In male insects, the structure analogous to a penis is known as

aedeagus An aedeagus (plural aedeagi) is a reproductive organ of male arthropods through which they secrete sperm from the testes during copulation with a female. It can be thought of as the insect equivalent of a mammal's penis, though the comparison ...

. The male copulatory organ of various lower invertebrate animals is often called the ''cirrus''. The

lesser water boatman The lesser waterboatman or lesser water boatman (''Corixa punctata'') is a water-dwelling insect of the order Hemiptera. Adults normally range in size from 5 to 15 mm long, and are found in ponds, lakes and sometimes even swimming pools. ...

's mating call, generated by rubbing the penis against the abdomen, is the loudest sound, relative to body size, in the animal kingdom. In 2010, entomologist Charles Linehard described ''

Neotrogla ''Neotrogla'' is a genus of barklice noted for its reversed sex roles and organs, traits shared by all species of the genus. Habitat ''Neotrogla'' are found in dry cave systems throughout Brazil. They feed primarily on bat guano. Description ...

'', a new genus of barkflies. Species of this genus have sex-reversed genitalia. Females have penis-like organs called gynosomes that are inserted into vagina-like openings of males during mating. In 2014, a detailed study of the insects reproductive habits led by Kazunori Yoshizawae confirmed that the organ functions similar to a penis – for example, it swells during sexual intercourse – and is used to extract sperm from the male.

Mollusks

The penis in most male Coleoid

cephalopods A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, an ...

is a long and muscular end of the gonoduct used to transfer spermatophores to a modified arm called a

. That, in turn, is used to transfer the spermatophores to the female. In species where the hectocotylus is missing, the penis is long and able to extend beyond the mantle cavity and transfers the spermatophores directly to the female. Deepwater squid have the greatest known penis length relative to body size of all mobile animals, second in the entire animal kingdom only to certain sessile

s Penis elongation in ''

Onykia ingens ''Onykia ingens'', the greater hooked squid, is a species of squid in the family Onychoteuthidae. It occurs worldwide in subantarctic oceans. Although ''O. ingens'' was long attributed to the genus ''Moroteuthis'', several authors have recently ...

'' may result in a penis that is as long as the mantle, head and arms combined. Giant squid of the genus '' Architeuthis'' are unusual in that they possess both a large penis and modified arm tips, although it is uncertain whether the latter are used for spermatophore transfer.

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 Steven Blankaart (24 October 1650, Middelburg, Zeeland, Middelburg – 23 February 1704, Amsterdam) was a Dutch physician, iatrochemist, and Entomology, entomologist, who worked on the same field as Jan Swammerdam. Blankaart proved the exist ...

defined the word ''penis'' as "the Yard, made up of two nervous Bodies, the Channel, Nut, Skin, and Fore-skin, etc." According t
Wiktionary
this term meant (among other senses) "rod" or "bar". As with nearly any aspect of the body involved in sexual or excretory functions, the penis is the subject of many slang words and

euphemism A euphemism () is an innocuous word or expression used in place of one that is deemed offensive or suggests something unpleasant. Some euphemisms are intended to amuse, while others use bland, inoffensive terms for concepts that the user wishes ...

s 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 A phallus is a penis (especially when erect), an object that resembles a penis, or a mimetic image of an erect penis. In art history a figure with an erect penis is described as ithyphallic. Any object that symbolically—or, more precisel ...

"'' (from Greek φαλλος) is sometimes used to describe the penis, although "phallus" originally was used to describe ''representations'', pictorial or carved, of the penis.

Heraldry

Pizzles are represented in

heraldry Heraldry is a discipline relating to the design, display and study of armorial bearings (known as armory), as well as related disciplines, such as vexillology, together with the study of ceremony, rank and pedigree. Armory, the best-known branch ...

, where the adjective ''pizzled'' (or ''vilené'') indicates that part of an animate charge's anatomy, especially if coloured differently.

References

Citations

General and cited references

Horses

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Marsupials

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Other animals

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External links

Kinsey Institute on the penis
{{Authority control Animal male reproductive system Articles containing video clips Sex organs

Vertebrates

Birds

Mammals

Artiodactyls

=Deer

Cetaceans

Perissodactyls

Carnivores

Bats

Rodents

Primates

=Humans

Marsupials

Monotremes

Others

Fish and reptiles

Invertebrates

Arthropods

Insects

Mollusks

Etymology

Heraldry

See also

References

Citations

General and cited references

Horses

Marsupials

Other animals

External links