1. Wilson TG: Diseases of the Ear, Nose and Throat in Children. London, William Heinemann Medical Books Ltd, 1962, p 226.
2. Behrendes J, Link R, Zöllner Z: Hals-Nasen-Ohren-Heilkunde, Band II/ Teil 1. Stuttgart, Georg Thieme Verlag, 1963, p 164.
3. Simpson JF, Robin IG, Ballantyne JC, A Synopsis of Otolaryngology. Bristol, John Wright & Sons Ltd, 1967, p 279.
4. Ballenger JJ: Diseases of the Nose, Throat and Ear, ed 11. Philadelphia, Lea & Febiger, 1969, p 217.
5. De Weese DD, Saunders WH: A Text Book of Otolaryngology, ed 4. St. Louis, C V Mosby Company, 1973, p 72.