The anus is located in the most end of the human digestive tract, located in the middle of the two sides of the buttocks, the female anus is located in the back of the vaginal opening, the anus due to the sphincter, the normal state of contraction, the shape of the front and back of a longitudinal fissure. Due to the contraction of the anus around the anus will show radial skin folds, local color is dark, is due to local pigmentation, some patients with more hair, will also appear in the anus around the hair. Normal perianal skin folds, but the general should be flat, there is no abnormal lumps, there is no local redness, swelling, heat, pain, etc. Although the anus is small, but because it is a defecation channel, so this place is also very much a variety of diseases. Common diseases are hemorrhoids, anal fissure, anal fistula, perianal abscess, sinusitis, perianal eczema and so on.