The anal canal is divided into anatomical and surgical anal canal, with the anatomical anal canal averaging 2.5cm in length in adults and the surgical anal canal averaging 4cm in length in adults. The anal canal is the end of the digestive tract, which is connected to the rectum on the top and the anus on the bottom, and is divided into anatomical anal canal and surgical anal canal. The anatomical anal canal refers to the part of the anal canal from the dentate line to the anal verge (the edge of the anus), while the surgical anal canal refers to the part from the anal verge to the plane of the anorectal ring, and there is some difference between the two. The dentate line is located at the junction of the skin of the anal canal and the mucosa of the rectum, and is a jagged shaped loop surrounded by the anal valve and the lower end of the anal column. The anorectal ring is the section of the rectum that passes through the pelvic septum to the anal verge.