The faces shown for comedy and tragedy were originally said to represent the two sides of Dionysus. Masks worn by actors to represent the gods allowed an imaginative portrayal of their persona. Also in early acting masks were used to embody the female character as women were not allowed to perform when theatre began. Dionysus was regarded as the 'god of the theatre' by the early Greeks... so the mask connection. Tragedy was seen to represent his sadness and comedy his joy and revelry. The nymph holding both here shows some poetic licence on the part of the mask designer. It looks like she is a blending of the muse of tragedy Melpomene and of Thailia the muse of comedy.