1. Johnston and Whillis (1949).Gray’s Anatomy, Longmans, London.
2. Morson, C. (1946).Proc. Roy. Soc. Med., xxxv, 287.
3. Simpson Smith, A. (1936).Brit. J. Surg., xxiv, 94, 309.
4. Wells, C. (1942).Proc. Roy. Soc. Med., xxxv, 290.
5. Barry (1942). Ibid., 292.