Baculum

The baculum (also penis bone, penile bone, or os penis) is a bone found in the penis of many placental mammals. It is absent in the human penis, but present in the penises of other primates, such as the gorilla and chimpanzee. The bone is located above the male urethra, and it aids sexual reproduction by maintaining sufficient stiffness during sexual penetration. The homologue to the baculum in female mammals is known as the baubellum or os clitoridis– a bone in the clitoris.

The word baculum meant "stick" or "staff" in Latin and originated from Greek: βάκλον, baklon "stick".

The baculum is used for copulation and varies in size and shape by species. Its characteristics are sometimes used to differentiate between similar species. A bone in the penis allows a male to mate for a long time with a female, which can be a distinct advantage in some mating strategies.

Mammals having a penile bone (in males) and a clitoral bone (in females) include various eutherians:

It is absent in humans, ungulates (hoofed mammals),elephants, monotremes (platypus, echidna),marsupials,lagomorphs,hyenas,sirenians, and cetaceans (whales, dolphins, and porpoises), among others.

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