1) WHO: Histological typing of oral and oropharyngeal tumors. Geneva, 1971, p17.
2) Jacobsson, P.A., Eneroth, C.M., et al.: Histological classification and grading of malignancy in carcinoma of the larynx. Acta Rad Ther Phy Bio 12: 1-8 1973.
3) Willen R., Nathanson, A., et al.: Squamous cell carcinoma of the gingiva. Acta Otolaryng 79: 146-154 1975.