Study of four heads
XVI century. Wash, Grey-brown ink, Pencil on brown paper.Not on display
The same four heads appear to the left, beneath the center, in one of the drawings from de Cambiaso Album series (no. 106, D01668). Another drawing from the same album contains multiple heads of this same type (no. 107, D01669)
Turner, Nicholas, From Michelangelo to Annibale Carracci. A century of Italian drawings from the Prado, Chicago, Art Services International, 2008, p.238