This "leaf " is actually a montage of vellum cuttings excised from one or more service books taken from the Sistine Chapel during the 1798 French occupation of Rome. These cuttings were brought to England by Luigi Celotti (1759–1843), who presumably created the montage and sold it at Christie's on 26 May 1825, lot 87. In the Celotti sale catalogue, William Ottley (1771–1836) listed it under Pope Gregory XIII and attributed it to Giulio Clovio (1498–1578). It was then in Ottley's own sale at Sotheby's (10 May 1838, lot 243). The dealer Leo Olschki wisely offered the leaf to Morgan, who had acquired Clovio's masterpiece, the Farnese Hours, three years earlier. If the portraits are not by Clovio (he was then quite old) they are certainly by an artist who came under his influence. The evangelists are Matthew, Mark, Luke and John.