1. Tomes, C.S. Dental Anatomy, ed. 5. London , J. A. Churchill, 1898, p. 24.
2. Boyde, A. The Structure and Development of Mammalian Enamel. Unpublished PhD dissertation, London University, 1964, p. 197.
3. Humphrey, J., and Wellings, A.W. Textbook of Dental Anatomy and Physiology. London, Arnold, 1923, p. 97.