1. Black, G.V. Operative Dentistry, 4:303-5. 7th ed. Chicago: Medico-Dental Publishing Co., 1936.
2. Goldman, M.H. Periodontia, p. 205, also see Fig. 148, p. 203. St. Louis: C. V. Mosby Co., 1942 . From NOYES, ScHoUR, and NoYEs, Dental Histology and Embryology.