abdominal regions, the nine topographic subdivisions of the abdomen, determined by four imaginary lines imposed over the anterior surface in a tic-tac-toe pattern. The upper horizontal line passes along the level of the cartilages of the ninth rib, the lower along the iliac crests. The two vertical lines extend on each side of the body from the cartilage of the eighth rib to the center of the inguinal ligament. The lines divide the abdomen into three upper, three middle, and three lower zones: right hypochondriac, epigastric, and left hypochondriac regions (upper zones); right lateral (lumbar), umbilical, and left lateral (lumbar) regions (middle zones); right inguinal (iliac), pubic (hypogastric), and left inguinal (iliac) regions (lower zones). Compare abdominal quadrant.
