The anorectum (anorectal canal) is supplied by the haemorrhoidal arteries and drained by the internal haemorrhoidal plexus of veins. Sphincteric support is provided by the internal sphincter, puborectalis muscle and the external sphincter.

The external sphincter is a continuation of the puborectalis muscle and is made up of three parts:

  • Deep
  • Superficial
  • Subcutaneous

These form a ring of muscle in the anus that has an important function in the maintenance of continence.

Tissue spaces lie between the muscles, and these spaces are potential sites of abscess and fistula formation [1,2].


Understanding the anatomy of the anorectal canal is vital in the assessment and management of patients with benign anorectal disease.