Following a survey of the anatomical characteristics of the rectum and the posterior part of the pelvic floor, a description is given of the fibrous sheath enveloping the rectum, and of the fibrous leaves and septa which traverse the adipose tissue of the subperitoneal space and the ischiorectal fossa. These fibrous structures contain the blood vessels, the lymphatics and the nerves, the distribution of which is described in detail. The fibrous structures, in which many smooth muscle fibres are present, not only enclose the vessels and nerves but also form the suspensory apparatus of the rectum.