The rectum is the final section of the large intestine (colon) that connects to the anus. Its main function is to store feces before elimination from the body. The rectum constitutes the final 12-15 cm of the large intestine, beginning at the terminal portion of the colon and ending at the short, narrow passage leading to the anus. The rectum is composed of three layers. The mucosa, the inner lining of the rectum, contains glands that secrete mucus to facilitate the passage of feces. The muscularis propria, the middle layer of the rectal wall, is composed of muscles responsible for contraction. The outermost layer is a fatty layer. In addition to these three layers, lymph nodes, part of the immune system, surround the rectum.