appendix, small, worm-shaped blind tube, about 3 in. (7.6 cm) long and 1/4 in. to 1 in. (.64-2.54 cm) thick, projecting from the cecum (part of the large intestine) on the right side of the lower abdominal cavity. The structure, also called the vermiform appendix, has no function in people and is considered a vestigial remnant of some previous organ or structure, having a digestive function, that became unnecessary to people in their evolutionary progress (see digestive system). Infection of accumulated and hardened waste matter in the appendix may give rise to appendicitis, the symptoms of which are severe pain in the abdomen, nausea, vomiting, fever, abdominal tenderness, and muscle spasm. A blood count usually shows a rise in the number of white corpuscles. Appendicitis may occur at any age, although it is more prevalent in persons under 40 years of age. The danger in appendicitis is that the appendix can rupture, either spontaneously or because the patient has injudiciously been given laxatives or an enema, and that the infection can spread to the peritoneum (see peritonitis). Surgery is indicated in appendicitis, preceded and followed by antibiotic therapy.

in full vermiform appendix

Vestigial hollow tube attached to the cecum of the large intestine. The human appendix, usually 3–4 in. (8–10 cm) long and less than 0.5 in. (1.3 cm) wide, has no digestive function. Its muscular walls expel their own mucous secretions or any intestinal contents that enter it. Blockage of the opening may prevent expulsion and cause appendicitis: fluids collect, bacteria propagate, and the appendix becomes distended and inflamed; tissue in the appendix begins to die, and the organ may burst, causing peritonitis. Its symptoms may begin with moderate pain in the upper abdomen, about the navel, or all over the abdomen. Nausea and vomiting may then develop. The pain may shift to the right lower abdomen. Fever is usually present but is seldom high in the early phases. Differentiating acute appendicitis from other causes of abdominal pain requires careful examination. Treatment is removal of the appendix (appendectomy).

Learn more about appendix with a free trial on Britannica.com.