The umbilicus is the fibrous remnant of the fetal attachment of the umbilical cord after birth.
All layers of the anterior abdominal wall fuse at the umbilical ring, a small round defect in the linea alba located just inferior to the midpoint between the xiphoid process of the sternum and the pubic symphysis. The overlying skin is adherent to the umbilicus, causing a depression that is more accentuated with greater body mass.
The fibrous cicatrix is a fusion of several peritoneal and fibrous structures including the:
- round ligament of the liver (ligamentum teres)
- median umbilical ligament (obliterated urachus)
- two medial umbilical ligaments (obliterated umbilical arteries)
- transversalis fascia
- umbilical fascia surrounding the urachal remnant
- parietal peritoneum
The umbilicus in the fetus transmits the umbilical arteries, umbilical vein, urachus
and the vitelline duct (in the first trimester). It closes a few days after birth and involutes.