Baculum

The baculum (also penis bone, penile bone or os penis) is a bone found in the penis of most mammals. It is absent in humans, equids, marsupials, lagomorphs, and hyenas, amongst others. It is used for copulation and varies in size and shape by species. Its characteristics are sometimes used to differentiate between similar species.

The oosik of Native Alaskan cultures is a polished and sometimes carved baculum of various large northern carnivores such as walruses. The raccoon baculum is sometimes worn as a luck or fertility charm.

The word baculum originally meant "stick" or "staff" in Latin. The homologue to the baculum in female mammals is known as the baubellum or os clitoridis.

Clellan S. Ford and Frank A Beach, Patterns of Sexual Behavior, p. 30 says "Both gorillas and chimpanzees possess a penile bone. In the latter species the os penis is located in the lower part of the organ and measures approximately three-quarters of an inch in length."

In humans, which lack the baculum and baubellum, the rigidity of the erection is provided entirely through blood pressure in the corpus cavernosum. Humans occasionally are born with the penile bone. It is generally surgically removed.

Examples
Animals with a penile bone include:
 * Primates (excluding humans)
 * Canids
 * Felids
 * Rats
 * Walruses

Raccoon penis bone
A raccoon penis bone is the baculum of a raccoon. It is sometimes used as a charm for luck or fertility.

Popular culture
Author JT LeRoy's story Sarah features raccoon penis bones, as does William Gibson's novel, Count Zero.

Oosik
Oosik is a term used in Alaska to describe the baculum (penile bone) of walruses, seals, sea lions, and polar bears. Sometimes as long as 60 cm (2 ft), it can be polished and used as a handle for knives and other tools. It is also frequently sold as a souvenir to tourists by Alaska Natives, the only people permitted to hunt the walrus today. In 2007 a 4.5 foot long fossilized penis bone from an extinct species of walrus, believed by the seller to be the largest in existence, sold for $8000.



Absence in humans
The zoologist Richard Dawkins speculated in 2006, that the loss of the bone in humans, when it is present in our nearest related species the chimpanzee, is probably a result of sexual selection by females looking for signs of good health in prospective mates. The reliance of the human penis solely on hydraulic means to achieve a rigid state makes it particularly vulnerable to blood pressure variation. Poor erectile function betrays not only physical states such as diabetes and neurological disorders but mental states such as stress and depression.

General references

 * Gilbert, Scott F. and Ziony Zevit. 2001. Congenital human baculum deficiency: The generative bone of Genesis 2:21–23. American Journal of Medical Genetics 101(3): 284–285.
 * Clellan S. And Frank A. Beach 1951   Patterns of Sexual Behavior Publisher: N.Y., Harper, and Paul B. Hoeber, Inc. Medical Books  (ISBN 0313223556)