The rectum (from the Latin rectum intestinum, meaning straight intestine) is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long. At its commencement its caliber is similar to that of the sigmoid colon, but near its termination it's dilated, forming the rectal ampulla. Role in human defecation The rectum intestinum acts as a temporary storage facility for feces. As the rectal walls expand due t… (More on Rectum)