abdomen The proper anatomical term for what is known colloquially as the belly, or as the ‘stomach’, especially when localizing an ache or pain. The abdomen is roofed by the diaphragm, which separates it from the thorax (chest). At the front and sides is the abdominal wall, of skin, fat and muscle, and at the back, the spine (vertebral column); this whole compartment is the abdominal cavity. ‘Cavity’ suggests an empty space, which it is not. It is completely filled with the abdominal organs: the stomach and intestines; the liver, gall bladder, pancreas, spleen, and kidneys. These are all covered by a thin membrane, continuous with that which also lines the inside of the abdominal wall (peritoneum). This encloses the peritoneal ‘cavity’ that normally contains only a film of fluid. The abdominal cavity and its peritoneal lining are continuous below with those of the pelvis.

Stuart Judge

abdomen
1. In vertebrates, the region of the body that contains the internal organs other than the heart and lungs. In Mammalia it is bounded anteriorly by the diaphragm.

2. In most arthropods, the hind region (tagma) of the body, which contains most of the digestive tract, the gonads, and the genital openings. In Crustacea, the abdomen bears limbs which are to a greater or lesser extent segmentally arranged and the abdomen is not homologous with that of arachnids and insects. The abdomen usually shows at least some trace of segmentation, though in the course of evolution this has been lost in all but one family of spiders.

3. In insects, the segments of the body that lie posterior to the thorax. The abdominal segments carry no limbs, although there are appendages (associated with reproduction) on the terminal segments in certain exopterygote and apterygote orders (e.g. Thysanura) non-terminal segments may bear appendages that in some insects function as gills. In the primitive state the abdomen consists of eleven segments, but this number may be very much reduced in advanced insects.

ab·do·men / ˈabdəmən; abˈdōmən/ • n. the part of the body of a vertebrate containing the digestive organs; the belly. In humans and other mammals, it is contained between the diaphragm and the pelvis. ∎  Zool. the posterior part of the body of an arthropod.DERIVATIVES: ab·dom·i·nal / abˈdämənl/ adj.

abdomen (ab-dŏm-ĕn) n. the part of the body cavity below the chest (see thorax), from which it is separated by the diaphragm. The abdomen contains the organs of digestion (stomach, liver, intestines, etc.), excretion (kidneys, bladder, etc.), and in women reproduction (ovaries and uterus). It is lined by a membrane, the peritoneum.
—abdominal (ăb-dom-i-năl) adj.

abdomen The posterior region of the body trunk of animals. In vertebrates it contains the stomach and intestines and the organs of excretion and reproduction. It is particularly well defined in mammals, being separated from the thorax by the diaphragm. In many arthropods, such as insects and spiders, it may be segmented.