ABDOMEN, in human anat omy, that portion of the body bounded above by the diaphragm, below by the pelvis, behind by the lumbar vertebra, and in front by a thin layer of muscles, the abdominal muscles. This cavity contains the chief organs of digestion and the genitourinary system. By reason of the movements of the diaphragm it is rhyth mically its size, and the move ments of the intestines somewhat modify its internal contour. For purposes of de scription and for localization the abdomen is divided by a tit-tat-toe figure into nine regions; the upper and lower horizontal lines passing at the lower level of the ribs and the upper bor ders of the pelvis. From above downward the middle squares are termed the epigastric, the umbilical, and hypogastric; to the sides of the epigastric regions are the right and left hypochondrium (under the ribs); the right and left lumbar flank, the central umbilical re gion, and the right and left iliac regions lie down in the pelvis on either side of the hypo gastric area. The general location of the ab dominal viscera in the various areas is of in terest. The liver lies up under the ribs in the right hypochondrium, stretching over the upper part of the epigastrium into the left hypo chondrium; the stomach lies mostly in the left hypochondrium and reaches into the epigas trium just below the sternum; the large intes tine starts in the right iliac region, the appen dix being there also, goes up the right lumbar into the lower portion of the right hypochon drium, crosses straight over, dipping slightly into the umbilical region, from the left hypo chondrium it descends into the left iliac re gion and then turns back into the centre and ends at the rectum. The small intestine occu
pies most of the umbilical region, extending out into the others. The pancreas lies just behind the lower end of the stomach in the epigastrium. The spleen lies higher up on the left side behind, resting on the 10th and 11th ribs; the kidneys are behind high up, in the hypochondriac lumbar region, just coming below the free borders of the ribs; most pains in the small of the back thought to be kidney pains are pains from constipated bowels; kidney pains are high up under the ribs behind. The genital organs lie in the hypogastric and right and left iliac re gions, the bladder low in front in the centre, the uterus slightly above in the centre, the ovaries to the right and left in the right and left iliac fossw.
In entomology, the whole body of an in sect behind the thorax. It usually consists of rings or short hollow cylinders, which are united by a joint or membrane, and in some cases, as in the grub of the chameleon fly, slide upon one another like the tubes of a tele scope. Sometimes it bears a sting or an ovi positor, though in the perfect insect no appen dages are found.
An abdominal ring is one of two oblong tendinous openings or rings existing in either groin, or in the right and left inguinal regions. Through these rings pass the sper matic cord in the one sex, and the circular ligament of the uterus in the other. Consult Taussig, F. J., 'Surgical Diseases of Abdo men' (1910) ; Gray, (1916).