 Especially for small personal books like the Book of Hours, the leather often extended sideways, which gave extra protection for the book when not in use - the loose edges could be wrapped round, and often buckles or laces enabled the book to be securely closed.In addition, when reading, the book could be held from outside the cover, so that the clean inside surface of the leather, rather than the thumbs of the reader, touched the pages.This stopped the pages acquiring the dirty patches in the lower margins that many medieval books have.