The rectal membrane is usually about 3 centimeters from the anus. The distal digestive tract of the human body includes the colon, rectum, anal canal, and the distal end of the anal canal is the anus, and the rectum includes four layers of tissues from the inside to the outside, including the mucous membrane layer, the submucous membrane layer, the muscular layer, and the plasma membrane layer, and the length of the anal canal is generally about 3 centimeters, and the lower end of the rectum is connected to the anal canal, so the rectal membrane is generally about 3 centimeters away from the anus. There is a possibility of lesions in the rectum, including polyps, inflammation, tumors, etc. If the lesions are low, when doing rectal fingerprinting, or when doing anoscopy, these tests are simple and easy to perform, and they can detect these lesions, and then further diagnosis and treatment can be carried out.