Page 233. " Now the serpent was more subtil than any beast of the fiel which the Lord God had made "

Chapter 17 Epigraph

Author: n/a

Work: Genesis 3:1

Page 249. " O that it were possible we might but hold some two days' conference with the dead... "

Chapter 18 Epigraph

Author: John Webster

Work: The Duchess of Malfi - Act 4 Scene 2

There is a decent enough summary and analysis on the Wikipedia page.