Collier's New Encyclopedia (1921)/Abdomen
ABDOMEN (1) That portion of the trunk which in man commences beneath, and in mammalia behind, the diaphragm, and terminates at the extremity of the pelvis. The abdominal cavity is the largest in the human body. It is lined with a serous membrane, called the peritoneum. It contains the liver, with the gall-bladder, under its right lobe, the stomach, the pancreas, the spleen, the two kidneys, the bladder and the intestines. The more highly organized of the inferior animals have a similar structure. (2) In entomology, the whole posterior division of the body of an insect, united to the thorax by a small knot or attachment, well seen in the wasp. It includes the back as well as the parts below. Externally it is made up of a series of rings.