The skeleton featured in the cover art is originally a feature in an oil painting by William Etty (1787-1849) entitled The Sirens and Ulysses (1837). It represents a scene from Homer’s The Odyssey in which Ulysses leads his men past the Sirens. According to mythology, sirens are creatures that lure sailors to shipwreck with their enchanting voices. Etty was particularly skilled at figure drawing and he modeled the dead and skeletonized bodies in his paintings after drawings he completed in the morgue.