post copulation genital grooming has also been observed. rodents the glans penis of the marsh rice rat is long and robust, averaging 7.3 mm (9⁄32 in) long and 4.6 mm (3⁄16 in) broad, and the baculum (penis bone) is 6.6 mm (1⁄4 in) long. 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. 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 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, 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. 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 and dorsal prostate glands. part of the end of the vesicular gland is irregularly folded, not smooth as in most oryzomyines. in pseudoryzomys, 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. in drymoreomys, 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 squirrels have long, thin, and narrow penises, without a prominent baculum. winkelmann's mouse 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 is attached to the anus in an unusual way, forming an anogenital invagination. primates external male genitalia of papio hamadryas and chlorocebus pygerythrus 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. 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 18 mm (11⁄16 in) 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 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 monkeys have a red penis with a black scrotum. male baboons and squirrel monkeys 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 main article: human penis wikimedia commons has media related to human penis. penis of a human, with pubic hair removed to show anatomical detail 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, the 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, 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 monotremes 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. when not in use, the penis is retracted inside a preputial sac in the cloaca. the male echidna's penis is 7 cm (3 in) 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 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 cm (2+1⁄2 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. wikimedia commons has media related to elephant penis. an adult elephant has the largest penis of any land animal. an elephant's penis can reach a length of 100 cm (40 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. during musth, a male elephant may urinate with his penis still in the sheath, which causes the urine to spray on the hind legs. 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 is sexually aroused, species determination is easier. its penis can be as long as 35 mm (1+1⁄2 in), 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 direction. fish and reptiles 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. due to evolutionary convergence, turtle and mammal penises have a similar structure. in some fish, the gonopodium, andropodium, and claspers are intromittent organs (to introduce sperm into the female) developed from modified fins. invertebrates arthropods 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. 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. 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 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. 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 barnacles penis elongation in onykia ingens 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 defined the word penis as "the yard, made up of two nervous bodies, the channel, nut, skin, and fore-skin, etc." according to 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 euphemisms for it, a particularly common and