Baculum ( Os Penis )

The baculum ( os penis , penile bone) is the penile heterotopic bone found in seven eutherian orders, including the Primates. It is the most varied bone as far as size and shape. The baculum is widely distributed in all families of primates, with the exception of the monogeneric infraorder Tarsiiformes. It is also lacking in five New World monkey genera and in Homo . Its interspecific variability in length can be related to body size, phylogenetic constraints, duration of intromission during copulation, and mating system. Penile complexity, as well as baculum length, increases in species with dispersed or polygynandrous mating systems, in which the female mates with multiple partners during the same fertile periods. It is likely that there are multiple functions of the baculum, such as providing support during prolonged intromissions, female genital stimulation, and/or sperm transport facilitation and delivery.