bac·u·lum 
(băkyə-ləm)
(băkyə-ləm)n. pl. bac·u·la or bac·u·lums
The bone of the penis of many mammals, including most rodents, carnivores, and nonhuman primates. Also called os penis.
[New Latin, from Latin, rod, stick; see bak- in the Appendix of Indo-European roots.]