Rectum直肠 Position: within pelvic cavity, extends from S3 to pelvic diaphragm Curves两个弯曲: Sagittal plane Sacral flexure直肠骶曲 convex bac kward Perineal flexure直肠会 阴曲 convex forward Bladder 图Rectum 直肠 Position: within pelvic cavity, extends from S3 to pelvic diaphragm. Curves两个弯曲： • Sagittal plane – Sacral flexure 直肠骶曲 convex backward – Perineal flexure 直肠会 阴曲 convex forward