1. Gibbons CP, Read NW. Anal hypertonia in fissures; cause or effect? Br J Surg 1986;73:443–5.
2. Klosterhalfen B, Vogel P, Rixen H, Mittermayer C. Topography of the inferior rectal artery: a possible cause of chronic, primary anal fissure. Dis Colon Rectum 1989;32:43–52.
3. Ball C. The rectum, its diseases and developmental defects. London: Hodder and Stoughton, 1908.
4. Motson RW, Clifton MA. Pathogenesis and treatment of anal fissure. In: Henry MM, Swash M, eds. Coloproctology and the pelvic floor. London: Butterworth, 1985:340–9.
5. Rankin FW, Bargen JA, Buie LA. The colon, rectum and anus. Philadelphia: WB Saunders, 1932:584–93.