The external anal sphincter is a random muscle, with circular and elliptical muscle bundles, starting from the tailbone and dividing into two strands at the back of the anal canal, going around the lower part of the anal canal to the front of the anal canal and ending at the perineum, which can be divided into subcutaneous, superficial and deep according to its depth. The internal anal sphincter is a non-random muscle, which is the thicker part of the inner ring muscle in the lower part of the rectum, and becomes the internal sphincter around the upper part of the anal canal, its width is about 3cm, and the lower 2cm is surrounded by the external sphincter, the role of the internal sphincter is to help defecation, and there is no sphincter anal function.