The large intestine comprises (1) the caecum and appendix, (2) ascending colon, (3) transverse colon, (4) descending colon, (5) sigmoid flexure, composed of the iliac colon and pelvic colon, and (6) the rectum and anal canal.

The length of the large intestine exclusive of the rectum and anal canal is 135 cm. (4 ft. 6 in. ) in the female, and 140 cm. (4 ft. 8 in.) in the male. If the anterior abdominal wall is removed the caecum and part of the ascending colon are visible, but in the upper part of the lumbar region the colon disappears, being overlaid by the small intestine. Having turned at the hepatic flexure, it again comes into view below the lower edge of the liver and passes superficially across the abdomen to disappear under the left costal margin to form the splenic flexure. It is not visible again until it reaches the region of the crest of the ilium, where it once more becomes superficial and follows the inguinal (Poupart's) ligament down to near its lower end, where it turns backward and upward to form the sigmoid loop which descends along the sacrum. In operating it is necessary to be able to distinguish large from small intestine.

Size

The large intestine at its commencement at the caecum may have a diameter of 7.5 cm. (3 in.), but it decreases in size, and, especially if empty, the descending colon and sigmoid flexure may only be 2.5 cm. (1 in.) in diameter. A distended part of the small intestine will be larger than a contracted part of the colon. Inasmuch as operations are frequently done for obstructive conditions which greatly enlarge the involved parts, it is unreliable to depend on size as distinguishing the large intestine. There are three longitudinal bands (taeeniae colt) on the colon, from 6 to 12 mm. (1/4 to 1/2 in.) wide, according to the amount of distention. One is anterior, another postero-external, and the third postero-internal. On the transverse colon they have the same relative position when the great omentum and colon are raised and turned upward. They all begin at the appendix and traverse the large intestine until the rectum is reached, where they blend together, forming a longitudinal layer which is weak at the sides and strong anteriorly and posteriorly.

Sacculation of the colon is produced by the longitudinal bands being one-sixth shorter than the rest of the tube. While sacculation tends to become less marked on distension, it is still a valuable means of identification. Dividing the longitudinal bands will cause the sacculation to disappear and the gut to lengthen.

Appendices epiploicae or the small tags of peritoneum containing fat, are found along the large intestine as far as the rectum. They are most numerous along the inner longitudinal band and the transverse colon.