Endpapers are the inside covers and facing pages of books. Today, endpapers are almost always blank. But our more sophisticated forebears made good use of endpapers by adding thematic illustrations to them. Amy Crehore alerted me to this nice gallery of endpapers. (Shown here: The Junior Instructor, Book 1 reprinted in 1962 but originally from 1923.) Link
Mark Frauenfelder is the founder of Boing Boing and the editor-in-chief of MAKE and Cool Tools. Twitter: @frauenfelder. Come and hear Mark speak at the ALA conference in Chicago on July 1.