Part of peculiar quality of Piero della Francesca's paintings stems from the fact that he placed his knowledge of natura phenomena in the service of expressing preternatual meaning. The particular form of a coral amulet on the neck of the Infant Christ in the Montefeltro Altarpiece (and the Senigallia Madonna) demonstrates this remarkable combination and reveals Piero's previously unsuspected knowledge of and interest in human anatomy. The article is the result of collaboration between Miriam Redleaf, M.D., an Otolaryngologist (head and neck surgeon) at the University of Chicago, and Marilyn Aronberg Lavin, Art Historian at Princeton University.