Rectum – is last part of large intestine, serves for accumulation and evacuation of faecal material. It begins at level of promontory and descends into true pelvis in front of sacrum. Rectum – S-shaped, wide in middle and narrow at the end. Upper part of the rectum in the pelvic cavity so is called pelvic part. It widens and form ampulla. Terminal part of rectum is called anal part or anal canal. Structure of the wall: rectal wall is composed of three coats: mucous, submucous and muscular. Due to developed layer of submucosa, the mucous coat – form numerous longitudinal folds. The part which has 8 longitudinal folds is called anal columns; depressions between them called – anal sinuses. Circular space between anal sinuses and anus is called haemorrhoidal zone. Muscular coat consists of 2 layers: an inner circular and an outer longitudinal. Inner layer increases in thickness in upper part of perineal part and form here inner sphincter (m. sphincter ani internus). Blood supply: medial and inferior rectal arteries, internal iliac vein. Lymph vessels: nodi lymphatici iliaci interni. Innervation: rectal plexus, pelvic splanchnic nerves, pudendal nerve.
The ischiorectal fossa is the fat-filled space located lateral to the anal canal and inferior to the pelvic diaphragm. It is somewhat prismatic in shape, with its base directed to the surface of the perineum, and its apex at the line of meeting of the obturator and anal fasciae. Contents of ischiorectal fossa: Fat; Pudendal canal; Inferior rectal vessels and nerves.