Endoscope (colonoscope) image of the interior of a normal human transverse colon. The appearance of the interior of the colon varies along its length. The triangular cross-section seen in the ascending & transverse colon is due to three bands of longitudinal muscle, the teniae coli, which run the length of the organ, from the base of the appendix to the rectum. The teniae help to form haustra, the compartment-like pouches along its length. The descending & sigmoid colon are more tubular in appearance, their haustra less pronounced. The fine pattern of blood vessels in the mucosa (the mucous membrane lining the interior) is also typical of a normal colon.