It is generally known that cutaneous horns often become malignant, the change taking place at the base, and being evidenced by ulceration, secretion, and induration (Fig. 5). .

Fig. 6.-A cutaneous horn first arose upon some senile warts. When the picture was taken, there was infiltration and ulceration at the base of the growth. Microscopical examination showed the presence of early cancer. (Heidings-feld's collection).