In giant anteaters, the (retracted) penis and testes are located internally between the rectum and urinary bladder. [137] About half of all penises in the US are circumcised, and half are uncircumcised (still have foreskin) — so both types are common. Some people call circumcised penises “cut,” and uncircumcised penises “uncut.”

Zeglin RJ. (2015). Assessing the role of masculinity in the transmission of HIV: a systematic review to inform HIV risk reduction counseling interventions for men who have sex with men. Veale, D., et al. (2014). Am I normal? A systematic review and construction of nomograms for flaccid and erect penis length and circumference in up to 15521 men. Small, Meredith F. (1993). Female Choices: Sexual Behavior of Female Primates. Cornell University Press. ISBN 978-0-8014-8305-9 . Retrieved 23 July 2013. Macdonald, D.W., ed. (2009). The Princeton Encyclopedia of Mammals. Princeton University Press. ISBN 978-0-691-14069-8. Likewise, an erect penis of 3.94 inches is in the 5 percentile, meaning that only 5 out of 100 would have a penis shorter than 3.94 inches.

Larry Vogelnest; Rupert Woods (18 August 2008). Medicine of Australian Mammals. Csiro Publishing. ISBN 978-0-643-09928-9. Archived from the original on 26 March 2014 . Retrieved 23 July 2013. Lienhard, Charles; Oliveira do Carmo, Thais; Lopes Ferreira, Rodrigo (2010). "A new genus of Sensitibillini from Brazilian caves (Psocodea: 'Psocoptera': Prionoglarididae)". Revue Suisse de Zoologie. 117 (4): 611–635. doi: 10.5962/bhl.part.117600. ISSN 0035-418X. Archived from the original on 2014-11-03. In Transandinomys talamancae, the outer surface of the penis is mostly covered by small spines, but there is a broad band of nonspinous tissue. [97]

Your penis and scrotum are the two parts of the male (or what’s typically called male) external sex anatomy (outside your body). England, Gary (15 April 2008). Fertility and Obstetrics in the Horse. John Wiley & Sons. ISBN 978-0-470-75041-4 . Retrieved 18 February 2014. Limited to no statistically significant correlation between penis size and the size of other body parts has been found in research. Some environmental factors in addition to genetics, such as the presence of endocrine disruptors, can affect penis growth.William F. Perrin; Bernd Wursig; J. G.M. Thewissen (26 February 2009). Encyclopedia of Marine Mammals. Academic Press. ISBN 978-0-08-091993-5. Archived from the original on 11 October 2013 . Retrieved 28 June 2013.

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. [107] Janet Leonard; Alex Cordoba-Aguilar R (18 June 2010). The Evolution of Primary Sexual Characters in Animals. Oxford University Press. ISBN 978-0-19-971703-3. Archived from the original on 11 October 2013 . Retrieved 20 July 2013. 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 Sometimes, an average-sized penis may appear small due because there is additional skin around it. People may refer to this as a buried penis, and surgery can resolve it. Bassert, Joanna M.; McCurnin, Dennis M. (1 April 2013). McCurnin's Clinical Textbook for Veterinary Technicians. Elsevier Health Sciences. ISBN 978-1-4557-2884-8 . Retrieved 18 February 2014.Michael L. Augee; Brett A. Gooden; Anne Musser (January 2006). Echidna: Extraordinary Egg-laying Mammal. Csiro Publishing. ISBN 978-0-643-09204-4. Archived from the original on 26 March 2014 . Retrieved 23 July 2013. Leonard Lee Rue III (2004). The Deer of North America: The Standard Reference on All North American Deer Species--Behavior, Habitat, Distribution, and More. LYONS Press. ISBN 9781592284658. Archived from the original on 2013-05-28 . Retrieved 2013-05-05. Hormone treatment, surgery, and other techniques can increase the size of a very small penis. However, these treatments carry risks, and most people do not have a small enough penis to warrant these options. Measurements vary, with studies that rely on self-measurement reporting a significantly higher average than those with a health professional measuring. As of 2015 [update], 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 13.12cm (5.17 inches) long, while the average circumference of an erect human penis is 11.66cm (4.59 inches). [2] A 1996 study of flaccid length found a mean of 3.5 inches (8.9cm) when measured by staff. [3] Flaccid penis length can sometimes be a poor predictor of erect length. An adult penis that is abnormally small but otherwise normally formed is referred to in medicine as a micropenis, with the cutoff usually being defined as around 3 inches (7.6 cm). A human penis, flaccid and erect. Flaccid length is a poor predictor for erect length. King, Anna (2001). "Discoveries about Marsupial Reproduction". Iowa State University Biology Dept. Archived from the original on September 5, 2012 . Retrieved 2012-11-22.