Rectum. Colonoscope (endoscope) view of a normal healthy rectum. This is a retroflexed (bent backwards) view of the rectum. The endoscope (black) can be seen entering through the anal sphincter. The rectum, the final part of the large intestine, is about 12cm in length and runs from the sigmoid colon to the anal canal. Faeces are stored in the rectum prior to defaecation. The anus, the opening of the anal canal, is guarded by two ring-like muscular sphincters (centre), which are contracted & closed except during defecation.