Complex sentence: The subject matter of the work is the mythological story of Perseus beheading Medusa, a hideous woman-faced Gorgon whose hair was turned to snakes and anyone that looked at her was turned to stone.
Split into simpler sentences: The subject matter of the work is the mythological story of Perseus beheading Medusa. Medusa was an ugly-faced woman whose hair was turned to snakes and anyone that looked at her was turned to stone.