Hypotext
Hypotext is an earlier text which serves as the source of a subsequent piece of literature, or hypertext. For example, Homer's Odyssey could be regarded as the hypotext for James Joyce's Ulysses.
The word was defined by the French theorist Gérard Genette as follows "Hypertextuality refers to any relationship uniting a text B (which I shall call the hypertext) to an earlier text A (I shall, of course, call it the hypotext), upon which it is grafted in a manner that is not that of commentary."