The sheet with the thumbprint is entitled The Cardiovascular System and Principal Organs of a Woman (around 1509-10). Although fingerprints have been found on other Leonardo drawings, the one on the medical sheet as "the most convincing candidate for an authentic Leonardo fingerprint" among the Queen's 550 or so Leonardos. – The Art Newspaper
SOURCE: ArtsJournal at 01:24PM on January 31, 2019