This bronze mule's head was originally part of a fulcrum (headrest) on a Roman couch. The mule is associated with Dionysus, the god of wine and feasting, indicated here by the panther (another Dionysiac attribute) skin around his neck.
Richter, Gisela M. A. 1926. Ancient Furniture: A History of Greek, Etruscan, and Roman Furniture. p. 132, fig. 314, Oxford: Clarendon Press.
Richter, Gisela M. A. 1966. The Furniture of the Greeks, Etruscans and Romans. p. 107, fig. 243, London: Phaidon Press.