The baculum (pl.: bacula), also known as the penis bone, penile bone, os penis, os genitale, or os priapi, is a bone in the penis of many placental mammals. It is absent from the human penis, but present in the penises of some primates, such as the gorilla and the chimpanzee. The baculum arises from primordial cells in soft tissues of the penis, and its formation is largely influenced by androgens. The bone lies above the urethra, and it aids sexual reproduction by maintaining stiffness during sexual penetration. The homologue to the baculum in female mammals is the baubellum (os clitoridis), a bone in the clitoris.