Solution

An anal sphincter is made of group of muscles at the end of the rectum that surrounds anus and regukate the release of stool. The anus has two sphincter muscles external and internal. The external anal sphincter provides voluntary control for defecation. As the rectum gradually fills with faeces at rest and after meals, the continuous tonic contraction of the external anal sphincter helps to prevent defecation. The internal anal muscle is not under voluntary control. It is controlled by autonomous nervous system.