The term cutaneous horn is not exact, as only in appearance does the conditions bearing this name resemble a real horn, and yet this resemblance is often so striking that no better term can be devised. There are several kinds of cutaneous horns, differing from one another in appearance, in causation and also in histologic structure: the filiform horn; the papillomatous horn, which is a papilloma encased in layers of horny epithelium; the verrucous horn, likewise so encased; a horn arising from the bowl of an open atheroma, and the horn, frequently multiple, arising from a nevus. THE FILIFORM HORN The simplest and the most frequently met with is the filiform horn, which resembles a wooden peg slowly growing out from the surface, usually of the face, and results from an error in one of the most interesting functions of the skin. The epithelial cells are constantly renewed by mitosis