premise: Michelangelo's greatest work here is reserved for two minor members of the family, Lorenzo's grandson, Lorenzo the Duke of Urbino, portrayed as a pensive Roman soldier above two allegorical figures of Dawn (female) and Dusk (male), and his son, Giuliano the Duke of Nemours, more warrior-like above figures of Night (female) and Day (male).
hypothesis: Michelangelo's best work was only for the head of the family.