The colon has a length of about 5 feet. Its greatest width, about 3 inches, is at its commencement, but it is everywhere much wider than the small intestine. Whereas the wall of the small intestine is smooth externally, the wall of the colon is sacculated. Three muscular bands constrict it longitudinally; circular bands at intervals of about 1 inch or 1½ inch throw it into pouches. It ascends on the right side, lying far back against the body-wall, to which it is bound by peritoneum, which in this part of its course covers only its anterior surface. Having touched the under side of the liver, it loops forwards and to the left side, crossing the middle line just above the umbilicus. On the extreme left side it touches the spleen, getting very near to the back of the abdominal cavity. It then descends on the left side, again bound to the body-wall by peritoneum, although not so closely as on the right side, until it reaches the inner lip of the crest of the hip-bone. From here onwards the fold of peritoneum which attaches it allows it a free movement. This portion of the large intestine, the sigmoid flexure, may even fall over into the right groin. Lastly it curls backwards into the pelvis, as the rectum.
Movement of the contents of the alimentary canal may be favoured by judicious pressure, or massage. From the description of the situation of its several parts given above, it will be understood that if the right hand be placed on the abdomen immediately beneath the ribs, with the fingers well round to the left side, the stomach will be covered. Pressure from left to right will tend to drive its contents towards the pyloric valve. The small intestine is so irregular in its course as to preclude the possibility of following it with the hand. Pressure first on one side and then on the other, with a general tendency to work from above downwards, tends to press forward its contents; but, owing to its circular form and strong muscular walls, it is not in much need of help. Very different is the position of the large intestine in this respect. Its calibre is much greater, its wall is sacculated, its contents comparatively firm. If the palm of the hand be placed above the right groin and pressure directed upwards, the cæcum coli and ascending colon are emptied. If pressure be directed from the extreme right side just below the ribs, across the middle line to the left side, the transverse colon is emptied. The descending colon needs pressure from above downwards on the left side; the sigmoid flexure, pressure above the left groin, downwards, and towards the middle line.