1. 1M. Ellis(1971 ) Disease of the Ear, Nose and Throat , vol 4 , pp. 333 -373 . Butterworths, London.
2. 2S. F. C. Thomson, and V. E. Negus(1937 ) Diseases of the Nose and Throat , p. 520 .Cassell, London.
3. 3O. Kleinsasser(1968 ) Microlaryngoscopy and Endolaryngeal Microsurgery , p. 30 .W. B. Saunders, Philadelphia.