The #baculum (also penis bone, penile bone, or os penis, or os priapi[1]) 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.[2][3] The bone is located above the male urethra,[4] 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.[5][6][7]
The baculum is used for copulation and varies in size and shape by species. Its evolution may be influenced by sexual selection, and its characteristics are sometimes used to differentiate between similar species.[9] A bone in the penis allows a male to mate for a long time with a female,[10][11] which can be a distinct advantage in some mating strategies.[12][13] The length of the baculum may be related to the duration of copulation in some species.[14][15] In carnivorans and primates, the length of the baculum appears to be influenced by postcopulatory sexual selection.[16] In some bat species, the baculum can also protect the urethra from compression.[17] In some mammalian species, such as #badgers[34][35] and raccoons (Procyon lotor), the baculum can be used to determine relative age. If a raccoon's baculum tip is made up of uncalcified cartilage, has a porous base, is less than 1.2 g (0.042 oz) in mass, and measures less than 90 mm (3.5 in) long, then the baculum belongs to a juvenile.[26]
