The
rectum (from the Latin , meaning
straight intestine) is the final straight portion of the
large intestine in some
mammals, and the
gut in others. The human rectum is about long, and begins at the rectosigmoid junction (the end of the sigmoid colon), at the level of the third sacral vertebra or the sacral promontory depending upon what definition is used. 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) or the
dentate line, again depending upon which definition is used. In humans, the rectum is followed by the
anal canal, before the gastrointestinal tract terminates at the
anal verge.