Rectal folds. Colonoscope (endoscope) view of the transverse rectal folds or valves known as Houston's folds. The first is situated near the beginning of the rectum on the left side, the middle fold (also known as Nelaton's fold) is the most prominent, and the final fold is the smallest and situated about 5 centimetres above 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 defecation.