The abdomen is a roughly cylindrical body portion extending between the inferior thoracic margin to the superior pelvic margin and the lower limbs.

The superior border of the abdomen is marked by the inferior thoracic aperture, which is closed by the diaphragm. Inferiorly, the deep abdominal wall is continuous with the pelvic wall at the pelvic inlet. Superficially, the inferior border of the abdominal wall is the superior margin of the lower limb.

The abdomen is a chamber enclosed by a musculoskeletal wall called the abdominal wall. The abdomen contains a single large peritoneal cavity, which is continuous with the pelvic cavity.