1. Sicher, H.: Orban's Oral Histology and Embryology, 6th ed, St. Louis: C. V. Mosby Co., 1966, pp 341-342.
2. Baron, R.: Anatomie Comparée des Mammiferes Domestiques, Vol 2, Lyon: Laboratoire d' Anatomie, École Nationale Vétérinaire, 1968, p 23.
3. May, N.D.S. : The Anatomy of the Sheep, Brisbane: University of Queensland Press, 1963, p 312.
4. Bloom, W., and Fawcett, D.W. : A Textbook of Histology, 9th ed, Philadelphia: W. B. Saunders Co., 1968, p 217.