Penis

Penis of an Asian elephant

Penis asiatischer Elefant
Penis Hinterbeine und Schwanz asiatischer Elefant

A penis (plural penises or penes /-niːz/) is the primary sexual organ that male animals use to inseminate sexually receptive mates (usually females and hermaphrodites) during copulation.[1] 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 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. Even within the Vertebrata there are morphological variants with specific terminology, such as hemipenes.

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.[2]

Vertebrates

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)[3] and Anatidae (ducks, geese and swans).[4] 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.[5] 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 lake duck (also called 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.

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.[6] 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.[6]

The lake duck 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.[7][8] 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.

Male and female emus are similar in appearance,[9] although the male's penis can become visible when it defecates.[10]

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.[11]

Mammals

Hundepenis
External male genitalia of a Labrador Retriever.

As with any other bodily attribute, the length and girth of the penis can be highly variable between mammals of different species.[12][13] In many mammals, the size of a flaccid penis is smaller than its erect size. In the realm of absolute size, the smallest vertebrate penis belongs to the common shrew (5 mm or 0.2 inches).

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

In mammals the penis is divided into three parts:[14]

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. 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.[15]

Even-toed ungulates (Artiodactyla)

The penises of even-toed ungulates are curved in an S-shape when not erect.[16] In bulls, rams and boars, the sigmoid flexure of the penis straightens out during erection.[17]

When mating, the tip of a male pronghorn's penis is often the first part to touch the female pronghorn.[18] The pronghorn's penis is about 5 inches (13 cm) long, and is shaped like an ice pick.[19] The front of a pronghorn's glans penis is relatively flat, while the back is relatively thick.[20] The male pronghorn usually ejaculates immediately after intromission.[21][22]

The penis of a dromedary camel is covered by a triangular penile sheath opening backwards,[23] and is about 60 cm (24 in) long.[24][25] 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.[26][27]

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.[28][14][29]

The male genitalia of mouse deer are similar to those of pigs.[30] A boar's penis, which rotates rhythmically during copulation,[31] is about 18 inches (46 cm) long, and ejaculates about a pint of semen.[32] 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.[33]

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.[34] Some deer species spray urine on their bodies by urinating from an erect penis.[35] One type of scent-marking behavior in elk is known as "thrash-urination,[36][37] which typically involves palpitation of the erect penis.[37][38][39] A male elk's urethra points upward so that urine is sprayed almost at a right angle to the penis.[37] A sambar stag will mark himself by spraying urine directly in the face with a highly mobile penis, which is often erect during its rutting activities.[40] Red deer stags often have erect penises during combat.[41]

Penises in Jars ( 4890599548
Penises of minke whales on display at the Icelandic Phallological Museum

Cetaceans' reproductive organs are located inside the body. Male cetaceans (whales, dolphins, and porpoises) have two slits, the genital groove concealing the penis and one further behind for the anus.[42][43][44][45] Cetaceans have fibroelastic penises, similar to those of Artiodactyla.[46] The tapering tip of the cetacean penis is called the pars intrapraeputialis or terminal cone.[47] The blue whale has the largest penis of any organism on the planet, typically measuring 8–10 feet (2.4–3.0 m).[48] Accurate measurements are difficult to take because its erect length can only be observed during mating,[49] which occurs underwater. 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.[50] On at least one occasion, a dolphin towed bathers through the water by hooking his erect penis around them.[51] Between male bottlenose dolphins, homosexual behaviour 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.[52]

Odd-toed ungulates (Perissodactyla)

Stallions (male horses) have a vascular penis. When non-erect, it is quite flaccid and contained within the prepuce (foreskin, or sheath).

Tapirs have exceptionally long penises relative to their body size.[53][54][55][56] The glans of the Malayan tapir resembles a mushroom, and is similar to the glans of the horse.[57] The penis of the Sumatran rhinoceros contains two lateral lobes and a structure called the processus glandis.[58]

Carnivorans

All members of Carnivora (except hyenas) have a baculum.[59]Canine penises have a structure at the base called the bulbus glandis.[60][61]

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.[62][63] 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.[64] In male spotted hyenas, as well as females, the base of the glans is covered with penile spines.[65][66][67]

Domestic cats have barbed penises, with about 120–150 one millimeter long backwards-pointing spines.[68] 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.[69][70] Male felids urinate backwards by curving the tip of the glans penis backward.[61][71] 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.[72]

The male fossa has an unusually long penis and baculum (penis bone), reaching to between his front legs when erect[73] withbackwards-pointing spines along most of its length.[74] The male fossa has scent glands near the penis, with the penile glands emitting a strong odor.[73]

The beech marten's penis is larger than the pine marten's, with the bacula of young beech martens often outsizing those of old pine martens.[75]

Raccoons have penis bones which bend at a 90 degree angle at the tip.[76] The extrusibility of a raccoon's penis can be used to distinguish mature males from immature males.[77][78]

Male walruses possess the largest penis bones of any land mammal, both in absolute size and relative to body size.[79][80]

The adult male American mink's penis is 2.2 in (5.6 cm) long, and is covered by a sheath. The baculum is well-developed, being triangular in cross section and curved at the tip.[81]

Bats

Males of Racey's pipistrelle bat 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 baculum (penis bone), the shaft is long and narrow and slightly curved.[82] The length of the penis and baculum distinguish P. raceyi from all comparably sized African and Malagasy vespertilionids.[83] In males, penis length is 9.6 to 11.8 mm (0.38 to 0.46 in) and baculum length is 8.8 to 10.0 mm (0.35 to 0.39 in).[84]

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.[85]

Rodents

The glans penis of the marsh rice rat is long and robust,[86] averaging 7.3 mm (0.29 in) long and 4.6 mm (0.18 in) broad, and the baculum (penis bone) is 6.6 mm (0.26 in) long.[87] As is characteristic of Sigmodontinae, the marsh rice rat has a complex penis, with the distal (far) end of the baculum ending in three digits.[88] The central digit is notably larger than those at the sides.[86] 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 and Oryzomys couesi among oryzomyines examined.[89] On the urethral process, located in the crater at the end of the penis,[90] a fleshy process (the subapical lobule) is present; it is absent in all other oryzomyines with studied penes except O. couesi and Holochilus brasiliensis.[91] The baculum is deeper than it is wide.[86]

In Transandinomys talamancae, the outer surface of the penis is mostly covered by small spines, but there is a broad band of nonspinous tissue.[92]

Some features of the accessory glands in the male genital region vary among oryzomyines. In Transandinomys talamancae,[93] 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 and dorsal prostate glands. Part of the end of the vesicular gland is irregularly folded, not smooth as in most oryzomyines.[94]

In Pseudorhyzomys, the baculum (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.[95]

In Drymoreomys, there are three digits at the tip of the penis, of which the central one is the largest.[96]

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.[97]

The glans penis of a male cape ground squirrel is large with a prominent baculum.[98]

Unlike other squirrel species, red squirrels have long, thin, and narrow penises, without a prominent baculum.[99][100]

Winkelmann's mouse can easily be distinguished from its close relatives by the shape of its penis, which has a partially corrugated glans.[101]

The foreskin of a capybara is attached to the anus in an unusual way, forming an anogenital invagination.[102]

Primates

External male genitalia of Papio hamadryas and Chlorocebus pygerythrus.

Papio hamadryas-adult penis-Lisbon 07
Chlorocebus-pygerythrus-private-parts

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.[103]

The penile morphology of some types of strepsirrhine primates has provided information about their taxonomy.[104] Male galago species possess very distinctive penile morphology that can be used to classify species.[105][106][107]

The northern greater galago penis is on average 18 mm (0.71 in) in length, with doubled headed or even tridentate spines pointing towards the body. They are less densely packed than in Otolemur crassicaudatus.[105][106][107] The penis of the ring-tailed lemur is nearly cylindrical in shape and is covered in small spines, as well as having two pairs of larger spines on both sides.[108]

The adult male of each vervet monkey species has a pale blue scrotum and a red penis,[109][110] and male proboscis monkeys have a red penis with a black scrotum.[111]

Male baboons and squirrel monkeys sometimes gesture with an erect penis as both a warning of impending danger and a threat to predators.[112][113] In male squirrel monkeys, this gesture is used for social communication.[114][114]

Humans

Penis with Labels
Penis of a human

The human penis is an external sex organ of male humans. It is a reproductive, intromittent organ 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, one on either side of the bulb; the body of the penis (corpus); and the epithelium of the penis consists of the shaft skin, the foreskin, and the preputial mucosa 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. The urethra, which is the last part of the urinary tract, traverses the corpus spongiosum, and its opening, known as the meatus /miːˈeɪtəs/, 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, and then onward to the penis.

An erection is the stiffening and rising of the penis, which occurs during sexual arousal, 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: removal of part or all of the foreskin for various cultural, religious, and more rarely medical reasons. There is controversy surrounding circumcision.

As of 2015, a systematic review of 15,521 men, and the best research to date on the topic, as the subjects were measured by health professionals, rather than self-measured, has 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).[115][116]

Marsupials

Most marsupials, except for the two largest species of kangaroos and marsupial moles[117] (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.[118]

Monotremes

Monotremes and marsupial moles are the only mammals in which the penis is located inside the cloaca.[119][120]

Male echidnas have a four-headed penis.[121] 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.[122] When not in use, the penis is retracted inside a preputial sac in the cloaca. The male echidna's penis is 7 centimetres (2.8 in) long when erect, and its shaft is covered with penile spines.[123] The penis is nearly a quarter of his body length when erect.[124] Each side of the bilaterally symmetrical, rosette-like, four-headed penis [similar to that of reptiles and 7 centimetres (2.8 in) in length] is used alternately, with the other half being shut down between ejaculations.[125][126]

Other mammals

The penis of the bush hyrax 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 6 centimetres (2.4 in) 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.[127]

An adult elephant has the largest penis of any land animal.[128] 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.[129] During musth, a male elephant may urinate with his penis still in the sheath, which causes the urine to spray on the hind legs.[130][131] An elephant's penis is very mobile, being able to move independently of the male's pelvis,[132] and the penis curves forward and upward prior to mounting another elephant.[66]

In giant anteaters, the (retracted) penis and testes are located internally between the rectum and urinary bladder.[133]

When the male armadillo Chaetophractus villosus is sexually aroused, species determination is easier. Its penis can be as long as 35 millimetres (1.4 in), and usually remains completely withdrawn inside a skin receptacle.[134] 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 direction.[135]

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.[136] Due to evolutionary convergence, turtle and mammal penises have a similar structure.[137]

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

Invertebrates

Arthropods

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

The record for the largest penis size 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 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 bugs.

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 which collect the spermatophore and insert it into the female.

Insects

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.

The lesser water boatman's mating call, generated by rubbing the penis against the abdomen, is the loudest sound, relative to body size, in the animal kingdom.[138]

In 2010, entomologist Charles Linehard described Neotrogla, 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.[139] 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.[140][141]

Mollusks

The penis in most male Coleoid cephalopods is a long and muscular end of the gonoduct used to transfer spermatophores to a modified arm called a hectocotylus. 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. Deep water 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 barnacles Penis elongation in Onykia ingens may result in a penis that is as long as the mantle, head and arms combined.[142][143] 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.[142]

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,[144] 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."[145]

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.[146]

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.

Human use of animal penises

Pizzles are represented in heraldry, where the adjective pizzled (or vilené[147]) indicates that part of an animate charge's anatomy, especially if coloured differently.

See also

References

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Bibliography

Horses

Marsupials

Other animals

External links

Bull

A bull is an intact (i.e., not castrated) adult male of the species Bos taurus (cattle). More muscular and aggressive than the female of the species, the cow, the bull has long been an important symbol in many cultures, and plays a significant role in both beef ranching and dairy farming, and in a variety of other cultural activities.

Dildo

A dildo is a sex toy, often explicitly phallic in appearance, intended for sexual penetration or other sexual activity during masturbation or with sex partners.

Erectile dysfunction

Erectile dysfunction (ED), also known as impotence, is a type of sexual dysfunction characterized by the inability to develop or maintain an erection of the penis during sexual activity. Erectile dysfunction can have psychological consequences as it can be tied to relationship difficulties and self-image.

A physical cause can be identified in about 80% of cases. These include cardiovascular disease, diabetes mellitus, neurological problems such as following prostatectomy, hypogonadism, and drug side effects. Psychological impotence is where erection or penetration fails due to thoughts or feelings; this is somewhat less frequent, in the order of about 10% of cases. In psychological impotence, there is a strong response to placebo treatment.

Treatment involves addressing the underlying causes, lifestyle modifications, and addressing psychosocial issues. In many cases, a trial of pharmacological therapy with a PDE5 inhibitor, such as sildenafil, can be attempted. In some cases, treatment can involve inserting prostaglandin pellets into the urethra, injecting smooth muscle relaxants and vasodilators into the penis, a penile prosthesis, a penis pump, or vascular reconstructive surgery. It is the most common sexual problem in men.

Erection

An erection (clinically: penile erection or penile tumescence) is a physiological phenomenon in which the penis becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, vascular, and endocrine factors, and is often associated with sexual arousal or sexual attraction, although erections can also be spontaneous. The shape, angle, and direction of an erection varies considerably in humans.

Physiologically, erection is triggered by the parasympathetic division of the autonomic nervous system, causing nitric oxide (a vasodilator) levels to rise in the trabecular arteries and smooth muscle of the penis. The arteries dilate causing the corpora cavernosa of the penis (and to a lesser extent the corpus spongiosum) to fill with blood; simultaneously the ischiocavernosus and bulbospongiosus muscles compress the veins of the corpora cavernosa restricting the egress and circulation of this blood. Erection subsides when parasympathetic activity reduces to baseline.

As an autonomic nervous system response, an erection may result from a variety of stimuli, including sexual stimulation and sexual arousal, and is therefore not entirely under conscious control. Erections during sleep or upon waking up are known as nocturnal penile tumescence (NPT). Absence of nocturnal erection is commonly used to distinguish between physical and psychological causes of erectile dysfunction and impotence.

The state of a penis which is partly, but not fully, erect is sometimes known as semi-erection (clinically: partial tumescence); a penis which is not erect is typically referred to as being flaccid, or soft.

Fellatio

Fellatio (also known as fellation, and in slang as blowjob, BJ, giving head, or sucking off) is an oral sex act involving the use of the mouth or throat, usually performed by a person on the penis of another person. If performed on oneself, the act is called autofellatio. Oral stimulation of the scrotum may also be termed fellatio, or colloquially as teabagging.Fellatio can be sexually arousing for both participants, and may lead to orgasm for the receiving partner. It may be performed by a sexual partner as foreplay before other sexual activities such as vaginal or anal intercourse, or as an erotic and physically intimate act of its own. Like most forms of sexual activity, oral sex creates a risk of contracting sexually transmitted infections (STIs/STDs); however, the risk is significantly lower than that of vaginal or anal sex, especially for HIV transmission.Most countries do not have laws banning the practice of oral sex, though some cultures may consider it taboo. People may also refuse to give or receive it due to negative feelings or sexual inhibitions. Commonly, people do not regard forms of oral sex as affecting the virginity of either partner, though opinions on the matter vary.

Foreskin

The foreskin is the double-layered fold of smooth muscle tissue, blood vessels, neurons, skin, and mucous membrane part of the penis that covers and protects the glans penis and the urinary meatus. It is also described as the prepuce, a technically broader term that also includes the clitoral hood in women, to which the foreskin is embryonically homologous. The highly innervated mucocutaneous zone of the penis occurs near the tip of the foreskin. The foreskin is mobile, fairly stretchable, and acts as a natural lubricant.

The foreskin of adults is typically retractable over the glans. Coverage of the glans in a flaccid and erect state varies depending on foreskin length. The foreskin is attached to the glans at birth and is generally not retractable in infancy. Inability to retract the foreskin in childhood should not be considered a problem unless there are other symptoms.The World Health Organization debates the precise functions of the foreskin, which may include "keeping the glans moist, protecting the developing penis in utero, or enhancing sexual pleasure due to the presence of nerve receptors".The foreskin may become subject to a number of pathological conditions. Most conditions are rare, and easily treated. In some cases, particularly with chronic conditions, treatment may include circumcision, a procedure where the foreskin is partially or completely removed.

Genital modification and mutilation

The terms genital modification and genital mutilation can refer to permanent or temporary changes to human sex organs. Some forms of genital alteration are performed on adults with their informed consent at their own behest, usually for aesthetic reasons or to enhance stimulation. However, other forms are performed on people who do not give informed consent, including infants or children. Any of these procedures may be considered modifications or mutilations in different cultural contexts and by different groups of people.

Glans penis

The glans penis is a structure at the distal end of the penis in male mammals. It is the sensitive bulbous structure at the end of the human penis, and is anatomically homologous to the clitoral glans of the human female. The glans penis may be smooth, spiny, elongated, or divided in other mammals.

Typically, the glans is completely or partially covered by the foreskin in humans, except in men who have been circumcised. The foreskin can generally be retracted over and past the glans, and may automatically retract during an erection. The glans is more commonly known as the "head" or the "tip" of the penis. The medical name comes from the Latin words glans ('acorn') and penis ('of the penis') – the Latin genitive of this word has the same form as the nominative.

Human penis

The human penis is an external male intromittent organ that additionally serves as the urinal duct. The main parts are the root (radix); the body (corpus); and the epithelium of the penis including the shaft skin and the foreskin (prepuce) covering the glans penis. The body of the penis is made up of three columns of tissue: two corpora cavernosa on the dorsal side and corpus spongiosum between them on the ventral side. The human male urethra passes through the prostate gland, where it is joined by the ejaculatory duct, and then through the penis. The urethra traverses the corpus spongiosum, and its opening, the meatus (), lies on the tip of the glans penis. It is a passage both for urination and ejaculation of semen. (See: male reproductive system.)

Most of the penis develops from the same tissue in the embryo as does the clitoris in females; the skin around the penis and the urethra come from the same embryonic tissue from which develops the labia minora in females. An erection is the stiffening and rising of the penis, which occurs during sexual arousal, though it can also happen in non-sexual situations. Spontaneous non-sexual erections frequently occur during adolescence and during sleep.

In its relaxed (flaccid, i.e. soft/limp) state, the shaft of the penis has the feel of a dense sponge encased in very smooth eyelid-type skin. The tip, or glans of the penis is darker in color, and covered by the foreskin, if present. In its fully erect state, the shaft of the penis is rigid, with the skin tightly stretched. The glans of the erect penis has the feel of a raw mushroom. The erect penis may be straight or curved and may point at an upward or downward angle, or straight ahead. It may also have a tendency to the left or right.

Measurements vary, with studies that rely on self-measurement reporting a significantly higher average than those with a health professional measuring. As of 2015, a systematic review of 15,521 men, and the best research to date on the topic, as the subjects were measured by health professionals, rather than self-measured, has 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). Neither age nor size of the flaccid penis accurately predicts erectile length.

The most common form of genital alteration is circumcision, removal of part or all of the foreskin for various cultural, religious and, more rarely, medical reasons. There is controversy surrounding circumcision.

Human penis size

The most accurate measurement of the size of a human penis can be derived from several readings at different times since there is natural minor variability in size depending upon arousal level, time of day, room temperature, frequency of sexual activity, and reliability of measurement. When compared to other primates, including large examples such as the gorilla, the human penis is thickest, both in absolute terms and relative to the rest of the body.

Measurements vary, with studies that rely on self-measurement reporting a significantly higher average than those with a health professional measuring. As of 2015, a systematic review of 15,521 men, and the best research to date on the topic, as the subjects were measured by health professionals, rather than self-measured, has 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). Flaccid penis length can sometimes be a poor predictor of erect length.

Most human penis growth occurs between infancy and the age of five, and between about one year after the onset of puberty and, at latest, approximately 17 years of age.A statistically significant correlation between penis size and the size of other body parts has not been found in research. Some environmental factors in addition to genetics, such as the presence of endocrine disruptors, can affect penis growth. An adult penis with an erect length of less than 7 cm (2.8 in), but otherwise formed normally, is referred to in medicine as a micropenis.

Marsupial

Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia and the Americas. A distinctive characteristic common to these species is that most of the young are carried in a pouch. Well-known marsupials include kangaroos, wallabies, koalas, possums, opossums, wombats, and Tasmanian devils. Some lesser-known marsupials are the dunnarts, potoroos and cuscuses.

Marsupials represent the clade originating from the last common ancestor of extant metatherians. Like other mammals in the Metatheria, they give birth to relatively undeveloped young that often reside in a pouch located on their mothers’ abdomen for a certain amount of time. Close to 70% of the 334 extant species occur on the Australian continent (the mainland, Tasmania, New Guinea and nearby islands). The remaining 100 are found in the Americas — primarily in South America, but thirteen in Central America, and one in North America, north of Mexico.

The word marsupial comes from marsupium, the technical term for the abdominal pouch. It, in turn, is borrowed from Latin and ultimately from the ancient Greek μάρσιππος mársippos, meaning "pouch".

Micropenis

Micropenis is an unusually small penis. A common criterion is a dorsal (measured on top) erect penile length of at least 2.5 standard deviations smaller than the mean human penis size, or smaller than about 7 cm (2 3⁄4 in) for an adult when compared with an average erection of 12.5 cm (5 in). The condition is usually recognized shortly after birth. The term is most often used medically when the rest of the penis, scrotum, and perineum are without ambiguity, such as hypospadias. Micropenis occurs in about 0.6% of males.

Penis enlargement

Penis enlargement, or male enhancement, is any technique aimed to increase the size of a human penis. Some methods aim to increase total length, others the shaft's girth, and yet others the glans size. Techniques include pills, hormones, massage, stretching, inflation, incision, injections, and implants. While some techniques are hoaxes, others may be somewhat effective, perhaps at high risk of complications.

Some surgical methods have the most evidence of effectiveness, whereas others have fairly frequent complications, sometimes severe, including scarring that lead, ultimately, to penis shrinkage or erectile dysfunction. Noninvasive methods have received little scientific study, and most lack scientific evidence of effectiveness, although scientific evidence supports some elongation by prolonged traction. Some quack products may improve penis erection, mistaken by consumers for penis enlargement.

Because of great risk and uncertainty, medical professionals are generally skeptical of penile enlargement and avoid attempting it. Medical doctors do treat micropenis as a medical condition, however, usually by surgery, which can be warranted to improve urinary or sexual function. Most men seeking penis enlargement have normal-size penises, and many may experience penile dysmorphophobia by underestimating their own penis size while overestimating the average size.

Penis removal

In ancient civilizations, the removal of the human penis was sometimes used to demonstrate superiority or dominance over an enemy. Armies were sometimes known to sever the penises of their enemies to count the dead, as well as for trophies. The practice of castration (removal of the testicles) sometimes involved the removal of all or part of the penis, generally with a tube inserted to keep the urethra open for urination. Castration has been used to create a class of servants or slaves called eunuchs in many different places and eras.

In Russia, men of a devout group of Spiritual Christians known as the Skoptsy were castrated, either undergoing "greater castration", which entailed removal of the penis, or "lesser castration", in which the penis remained in place, while Skoptsy women underwent mastectomy. These procedures were performed in an effort to eliminate lust and to restore the Christian to a pristine state that existed prior to original sin.

In the modern era, removing the human penis for any such activity is very rare (with some exceptions listed below), and references to removal of the penis are almost always symbolic. Castration is less rare, and is performed as a last resort in the treatment of androgen-sensitive prostate cancer.

Phallus

A phallus is a penis (especially when erect), an object that resembles a penis, or a mimetic image of an erect penis.

Any object that symbolically—or, more precisely, iconically—resembles a penis may also be referred to as a phallus; however, such objects are more often referred to as being phallic (as in "phallic symbol"). Such symbols often represent fertility and cultural implications that are associated with the male sexual organ, as well as the male orgasm.

Priapism

Priapism is a condition in which a penis remains erect for hours in the absence of stimulation or after stimulation has ended. There are three types: ischemic (low-flow), nonischemic (high-flow), and recurrent ischemic (intermittent). Most cases are ischemic. Ischemic priapism is generally painful while nonischemic priapism is not. In ischemic priapism, most of the penis is hard; however, the glans penis is not. In nonischemic priapism, the entire penis is only somewhat hard. Very rarely, clitoral priapism occurs in women.Sickle cell disease is the most common cause of ischemic priapism. Other causes include medications such as antipsychotics, SSRIs, and blood thinners, as well as drugs such as cocaine and cannabis. Ischemic priapism occurs when blood does not adequately drain from the penis. Nonischemic priapism is typically due to a connection forming between an artery and the corpus cavernosum or disruption of the parasympathetic nervous system resulting in increased arterial flow. Nonischemic priapism may occur following trauma to the penis or a spinal cord injury. Diagnosis may be supported by blood gas analysis of blood aspirated from the penis or an ultrasound.Treatment depends on the type. Ischemic priapism is typically treated with a nerve block of the penis followed by aspiration of blood from the corpora cavernosa. If this is not sufficient, the corpus cavernosum may be irrigated with cold, normal saline or injected with phenylephrine. Nonischemic priapism is often treated with cold packs and compression. Surgery may be done if usual measures are not effective. In ischemic priapism, the risk of permanent scarring of the penis begins to increase after four hours and definitely occurs after 48 hours. Priapism occurs in about 1 in 20,000 to 1 in 100,000 males per year.

Sex toy

A sex toy is an object or device that is primarily used to facilitate human sexual pleasure, such as a dildo or vibrator. Many popular sex toys are designed to resemble human genitals and may be vibrating or non-vibrating. The term sex toy can also include BDSM apparatus and sex furniture such as slings; however, it is not applied to items such as birth control, pornography, or condoms. Alternative expressions include adult toy and the dated euphemism marital aid, although "marital aid" has a broader sense and is applied to drugs and herbs marketed to supposedly enhance or prolong sex. Sex toys are most commonly sold at a sex shop, but they may also be sold in a pharmacy/chemist store, a pornographic DVD store, or head shop. Today's sex toys are available in almost all countries for male and females.

Sexual intercourse

Sexual intercourse (or coitus or copulation) is principally the insertion and thrusting of the penis, usually when erect, into the vagina for sexual pleasure, reproduction, or both. This is also known as vaginal intercourse or vaginal sex. Other forms of penetrative sexual intercourse include anal sex (penetration of the anus by the penis), oral sex (penetration of the mouth by the penis or oral penetration of the female genitalia), fingering (sexual penetration by the fingers), and penetration by use of a dildo (especially a strap-on dildo). These activities involve physical intimacy between two or more individuals and are usually used among humans solely for physical or emotional pleasure and can contribute to human bonding.There are different views on what constitutes sexual intercourse or other sexual activity, which can impact on views on sexual health. Although sexual intercourse, particularly the variant coitus, generally denotes penile–vaginal penetration and the possibility of creating offspring, it also commonly denotes penetrative oral sex and penile–anal sex, especially the latter. It usually encompasses sexual penetration, while non-penetrative sex has been labeled "outercourse", but non-penetrative sex may also be considered sexual intercourse. Sex, often a shorthand for sexual intercourse, can mean any form of sexual activity. Because people can be at risk of contracting sexually transmitted infections during these activities, safe sex practices are advised, although transmission risk is significantly reduced during non-penetrative sex.Various jurisdictions have placed restrictive laws against certain sexual acts, such as incest, sexual activity with minors, prostitution, rape, zoophilia, sodomy, premarital and extramarital sex. Religious beliefs also play a role in personal decisions about sexual intercourse or other sexual activity, such as decisions about virginity, or legal and public policy matters. Religious views on sexuality vary significantly between different religions and sects of the same religion, though there are common themes, such as prohibition of adultery.

Reproductive sexual intercourse between non-human animals is more often called copulation, and sperm may be introduced into the female's reproductive tract in non-vaginal ways among the animals, such as by cloacal copulation. For most non-human mammals, mating and copulation occur at the point of estrus (the most fertile period of time in the female's reproductive cycle), which increases the chances of successful impregnation. However, bonobos, dolphins and chimpanzees are known to engage in sexual intercourse regardless of whether or not the female is in estrus, and to engage in sex acts with same-sex partners. Like humans engaging in sexual activity primarily for pleasure, this behavior in these animals is also presumed to be for pleasure, and a contributing factor to strengthening their social bonds.

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" neck, as well as a somewhat more muscular physique as compared to female horses, known as mares, and castrated males, called geldings.

Temperament varies widely based on genetics, and training, but because of their instincts as herd animals, they may be prone to aggressive behavior, particularly toward other stallions, and thus require careful management by knowledgeable handlers. However, with proper training and management, stallions are effective equine athletes at the highest levels of many disciplines, including horse racing, horse shows, and international Olympic competition.

The term "stallion" dates from the era of Henry VII, who passed a number of laws relating to the breeding and export of horses in an attempt to improve the British stock, under which it was forbidden to allow uncastrated male horses to be turned out in fields or on the commons; they had to be "kept within bounds and tied in stalls." (The term "stallion" for an uncastrated male horse dates from this time; stallion = stalled one.) "Stallion" is also used to refer to males of other equids, including zebras and donkeys.

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