urachus
A fibrous remnant of the allantoic stalk, a narrow fetal canal connecting the apex of the urinary bladder with the umbilicus located in the space of Retzius, between the transversalis fascia anteriorly and the peritoneum posteriorly. its lumen is normally obliterated during development, transforming the urachus into a solid cord, a functionless remnant that persists throughout life as the median umbilical ligament; failure of complete lumen obliteration may result in distinct congenital urachal remnant anomalies[MP].