The baculum (also penis bone, penile bone or os penis) is a bone found in the penis of most placental mammals. It is absent in humans, but present in other primates, such as the gorilla and chimpanzee. The bone aids sexual intercourse by maintaining sufficient stiffness during sexual penetration. The female equivalent is the os clitoridis - a bone in the clitoris.
Read more about Baculum: Purpose, Presence in Mammals, Absence in Humans, Cultural Significance