The urachus is an embryological canal connecting the urinary bladder of the fetus with the allantois, a structure that contributes to the formation of the umbilical cord. The lumen (inside) of the urachus is normally obliterated during embryonic development, transforming the urachus into a solid cord, a functionless remnant. The urachus lies in the space of Retzius, between the transversalis fascia anteriorly and the peritoneum posteriorly.
The vesico-urethral portion of the urogenital sinus
absorbs the ends of the Wolffian ducts
and the associated ends of the renal diverticula
, and these give rise to the trigone of the bladder
and part of the prostatic urethra
The remainder of the vesico-urethral portion forms the body of the bladder and part of the prostatic urethra; its apex is prolonged to the umbilicus
as a narrow canal, which later is obliterated and becomes the median umbilical ligament
Note: The two medial umbilical ligaments
are the obliterated umbilical arteries
Failure for the lumen of the urachus to be filled in leaves a patent (open) urachus. The telltale sign is leakage of urine through the umbilicus. A patent urachus needs to be surgically removed.