The allantois is a fetal membrane which develops from the hindgut. Externally it helps to form the placenta and umbilical cord, and internally the urinary bladder develops as a dilatation of its distal end.
The intra-abdominal portion of the allantois, between the umbilicus and the bladder, is the urachus. In normal development this remains as the middle umbilical ligament, which is a cord passing from the apex of the bladder along the posterior surface of the anterior abdominal wall to the umbilicus.
In a small number of cases the obliteration of this canal is not completed at birth, and several types of anomaly may result. The condition has been discovered twice as often in males as in females. It is probably most frequently found in infants at birth or after separation of the umbilical stump. It may first manifest itself in the baby as some form of irritation about the
SAWYER CF. CYSTS OF THE URACHUS. Arch Surg. 1945;50(3):174-176. doi:10.1001/archsurg.1945.01230030180008