**3. Definition**

An anal fissure is a linear, longitudinal split in the lining of the distal anal canal, extending from below the dentate line to the anal verge. They are usually very painful because of their somatic innervations, the pain resulting from spasm of the anal sphincter in response to stretching and tearing during passage of stool. A well developed anal fissure rests directly over the internal sphincter and the circular fibers of this sphincter are visible on the floor of the fissure on naked eye inspection.
