In the embryo, the endodermal alimentary tract ends as a blind receptacle called the cloaca; this has an anterior diverticulum called the allantois (urachus). The mesonephric duct (adult vas deferens) grows caudally and opens into the anterior part of the cloaca (Fig. 551). The ureter develops as an outpouching of the mesonephric duct, the two for a period ending in one terminal duct. This common duct subsequently is absorbed into the wall of the bladder and the prostatic urethra, with the result that the ureter and the vas deferens eventually have separate openings. A mesodermal septum (urorectal septum) divides the cloaca into an anterior, urogenital part and a posterior, intestinal part. The cloaca has a sphincter, also divided into an anterior portion, which becomes the superficial transversus perineus, the bulbospongiosus, the ischiocavernosus and the urogenital diaphragm; the posterior part of the sphincter becomes the external sphincter ani.
KeywordsSphincter Urethra Ischial Tuberosity Perineal Body Corpus Spongiosum Internal Pudendal Artery
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