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a part of the urogenital system in the males of certain vertebrates, for example, elasmobranchs and mammals. The uterus masculinus develops in the embryo from the lower part of the müllerian duct. The mammalian uterus masculinus usually has a small, bicorn cavity that shares a common opening into the urogenital canal with the deferent ducts and the prostate gland. In a number of animals, including primates, rodents, and lagomorphs, the uterus masculinus becomes the prostatic utricle, which fills the prostate gland with secretions during sexual activity. In some Odontoceti (toothed whales), the uterus masculinus is not connected with the cavity of the urogenital canal and persists either as cordlike strands or as irregular closed cavities filled with lymph.