This terracotta antefix with the head of Medusa originally decorated the edge of a roof of a building. The head of Medusa, a frequently featured device, would have been appropriate along the facade of a building, warding off any approaching evil.
Richter, Gisela M. A. 1928. "Recent Accessions of the Classical Department: Bronzes, Terracottas, Glass, Jewelry." Bulletin of the Metropolitan Museum of Art, 23(3): p. 82.
Richter, Gisela M. A. 1953. Handbook of the Greek Collection. p. 179, pl. 19d, Cambridge, Mass.: Harvard University Press.