narrow longitudinal fold of mucosa on the posterior wall of the male urethra, extending from the uvula of the bladder through the prostatic urethra; when distended, it may serve to prevent the passage of the semen backward into the bladder; on either side of the male urethral crest is a slightly depressed fossa, the prostatic sinus, the floor of which is perforated by the orifices of the prostatic ducts from the lateral lobes of the prostate; the ducts of the middle lobe open behind the crest; at the forepart of the crest, below its summit, is a median elevation, the colliculus seminalis, upon or within the margins of which are the orifices of the prostatic utricle and the slit-like openings of the ejaculatory ducts[MP] [ ]