While in the mare's womb, the urachus is part of the urinary system and extends from the urinary bladder through the umbilical cord and opens in the allantoic cavity where much of the fluids surrounding the fetus are found. Normally, the urachus is broken with the umbilical cord at birth and closes at this time or soon after. The structure in the abdomen of the foal will wither and become a ligament that ties the bladder to the floor of the pelvis and abdomen. Many diseases of the newborn involve improper closure or infection of the urachus and other structures of the umbilical cord. This article discusses the anatomy, diseases, diagnosis, and treatment of disease in the umbilical cord of the newborn.