SMALL.
The ileum ends at the right iliac region in the large intestine, which is from 5 to 6 ft. in length. It begins at the pouch called the blind gut (caput ciceum coli) or cul de sad (see C.Ecum), which has a small worm-like appendage (appendix veriniformis); a double valve guards the opening of the small into the large intestine. The colon passes upwards on the right side to below the liver (ascending colon), then crosses from the right hypochondrium across the upper umbilical to the left hypochondrium (transverse colon), then descends to the left iliac fosse (descending colon), when it bends twice like an S (sigmoid flexure), and then joins the rectum at the left margin of the true pelvis. The colon is distinguished by its pouched or sacculated appearance, the sacs being separated by three flat bands of longitudinal muscular fibers. The peritoneum only covers it in parts. See COLON. The rectum is not sacculated, but its muscular coat
becomes much thicker ; at its lower. end the longitudinal fibers stop, but the muscular become more numerous, forming the internal sphincter muscle. The rectum is not straight, but takes a curved course.
The A. C. thus consists of a continuous passage lined by mucous membrane, which rests on a fibrous and muscular basement. Its length is generally about five or six times the length of the body, or, in other words, about 30 ft. It begins below the base of the skull and passes through the thorax, abdomen, and pelvis, and consists shortly of the mouth, pharynx, cesophagns, stomach, small intestine, and large intestine. The above is the description of the A. C. in human anatomy ; its parts are variously modified in different animals,'as will be found in the articles on its several subdivisions.