Umbilicus

Recommended video: Surface anatomy of the abdomen and the lower extremity [13:14]

Overview of the surface anatomy landmarks found in the abdomen and lower limbs.

The umbilicus forms the fibrous remnant of the fetal-maternal connection, the umbilical cord. 

During embryonic development, the umbilical cord acts as a conduit between mother and baby and creates a channel which allows blood to flow between the placenta and fetus. After birth, the umbilical cord detaches and a fibrous scar, the umbilicus, remains. The umbilicus contains the obliterated orifices of the three umbilical vessels (one vein, two arteries). Before birth, the umbilical vein functions as the source of oxygenated blood to the fetus via the liver and ductus venosus. In contrast, the paired umbilical arteries, branches of the internal iliac artery, carry waste materials and unoxygenated blood to the placenta.

The umbilicus is composed of four distinct anatomical structures: the mamelon, cicatrix, cushion and furrows.

• The mamelon is the area of the central hump of the umbilicus.
• The cicatrix forms the dense scar and is a fusion of several peritoneal and fibrous structures (round ligament of liver, median umbilical ligament, two medial umbilical ligaments, transversalis fascia, umbilical fascia and parietal peritoneum).
• The cushion of the umbilicus is the slightly raised skin margin which surrounds the mamelon and cicatrix.
• Finally, furrows stand for the depressions inside the cushion, surrounding the mamelon.

The layers of the anterior abdominal wall fuse at the umbilical ring (final part of the abdomen to close during embryonic development) which surrounds the umbilicus.

The umbilicus acts as an important anatomical landmark of the abdomen as its position is relatively consistent between individuals. The umbilicus is located along the midline of the anterior abdominal wall at the level of the intervertebral discs between L3 and L4. It is also used to separate the abdomen into quadrants and regions.