The literary work of beloved children's book author Dr. Seuss wasn't all cats in hats and truffula trees.

Tucked away in his canon of books is Theodore Seuss Geisel's adult picture book: The Seven Lady Godivas: The True Facts Concerning History's Barest Family.

According to Maria Popova of Brain Pickings, when Seuss left Vanguard for Random House in 1939, he asked his publisher to allow him one adult book. The resulting picture book is based on the legend of Lady Godiva, who supposedly rode naked on a horse through Coventry, England, after her husband, Leofric, Earl of Mercia, refused to lower taxes.

Seuss' story features seven nudist sisters who, following the death of their father, refuse to get married until each has brought to light "some new and worthy Horse Truth, of benefit to man."

According to Popova, however, the book was a flop and only 2,500 copies sold. It is now out of print, but copies are available (for a hefty chunk of cash) online.

In honor of the late author's birthday on Monday, take a peek inside Seuss' nude picture book.