The layers of the intestinal wall, starting from within comprise mucosa, submucosa, muscle coat, and serosa or peritoneum. The mucosa of the colon is lined with columnar epithelial cells with crypts but no villi, so that the surface is flat. The mucosa is full of goblet cells (Figure 2). A variety of cells, mainly lymphocytes and macrophages, are found in the lamina propria. The lower crypt includes the replicative compartment. Maturing cells migrate up the crypt and reach the surface epithelium within a matter of days where they undergo apoptosis. The rectum is about 15 cm long. Its interior is divided by three crescentic circular muscles producing shelf like folds. These are the rectal valves that can be seen at sigmoid copy. The anal canal has an internal and an external sphincter