With anal canal rectum forms an angle of

The lumen of the rectum terminates at the pelvic floor and is continued, downwards and posteriorly, as the anal canal, passing through the levator ani muscle sheet and surrounded by the internal and external anal sphincters. The anal canal is 2.5 to 5 cm in length and 3 cm in diameter when distended. The axis of the rectum forms almost a right angle (average 82 degrees) with the axis of the anal canal. It has been established by radiological studies that the anal canal is an antero-posterior slit in the resting state. Ref -pubmed.com