Stored away in the rare-book library at Yale University is a late-medieval manuscript written in a cramped but punctilious script and illustrated with lively line drawings that have been painted over, at times crudely, with washes of color. These illustrations range from the fanciful (legions of heavy-headed flowers that bear no relation to any earthly variety) to the bizarre (naked and possibly pregnant women, frolicking in what look like amusement-park waterslides from the fifteenth century...