Rectum

The rectum is the final portion of the large intestine. The human rectum is about 12 centimetres (4.7 in) long and begins at the rectosigmoid junction (the end of the sigmoid colon), around the level of the third sacral vertebra. Its caliber is similar to that of the sigmoid colon at its commencement, but it is dilated near its termination, forming the rectal ampulla. It terminates at the level of the anorectal ring (the level of the puborectalis sling). The rectum is followed by the anal canal, before the gastrointestinal tract terminates at the anus.