1. Kopetzky Samuel J.: Surgery of the Ear, Thos. Nelson and Sons, New York, 1938, p. 55.
2. Bast Theodore H., Anson Barry J.: The Temporal Bone and the Ear, First Ed., Chas. C. Thomas, Springfield, Illinois, 1949, p. 43.
3. Law Frederick M.: Annals of Roentgenol., Vol. I, The Mastoids, 2nd Ed., Paul B. Hoeber, New York, 1929, Plate XIII, p. 21.