Cancer of the colon. Coloured barium enema X-ray of the human abdomen showing a cancer of the ascending colon; the tumour appears as the oval shadow over the right pelvic bone (left on image). Opaque to X- rays, barium is given orally (barium meal) for investigations of the oesophagus, stomach & duodenum and rectally (as a barium enema) to examine the rectum & colon. The colon (large intestine) consists of four sections - the ascending, transverse, descending and sigmoid colons. Here, the ascending colon rises at left, its transverse (horizontal) section appears in centre, and the descending part at right, which connects with the rectum via the sigmoid colon.