Michael Barrier has a fascinating essay on the story behind the story of Dumbo. The first version of Dumbo was copyrighted in 1939, but not in normal book form. Instead the thing stated life on an odd and interesting device from the late 1930’s called a “Roll-A-Book”. Barrier’s piece goes in depth with lots of quotes from the people involved, research in the Disney vaults, and even a look from the patent office on what the Roll-A-Book may have looked like.