Just below Jean de Dinteville and Georges de Selve is a distorted skull that appears normally if viewed from below.  
Its tile floor borrows its design from the mosaic floor of Westminster Abbey.  Sometimes seen as an allusion to Plutarch's Parallel Lives, which had recently been translated by one of its subjects, it includes Peter Apian's book on accounting as one of the representatives of the quadrivium on display.  This is on one of the shelves in the back, which also hold a sundial and a globe.  Just below Jean de Dinteville and Georges de Selve is a distorted skull that appears normally if viewed from below.  FTP, name this portrait by Hans Holbein depicting two representatives of Francis I in London.
Its tile floor borrows its design from the mosaic floor of Westminster Abbey.  
The (French) Ambassadors