In Greek mythology, the satyr Marsyas found an enchanted flute that was cursed by Athena. He picked it up and found that it played to perfection on its own accord. Marsyas went around playing the flute and people heralded him for playing better than Apollo, the god of music. When Apollo got wind of this, he challenged Marsyas to a contest, with the Muses acting as judges. Apollo played his lyre and Marsyas his flute, while the audience was delighted by both. Apollo upped the game by suggesting they both play their instruments upside down and sing at the same time. Apollo successfully did so while Marsyas floundered and lost the contest. As a punishment for losing and for his hubris, Marsyas was flayed and his skin was nailed to a tree.
Sheppard has given us a defeated Marsyas on the ground surrounded by the Muses (the girls) and Athena playing a smoking cello, while the bust of Apollo (with his bloody flaying knife) looks on.