"Lafater aurait dit que ne n'ai pas la bosse de la paternité"

 'Lavater would have said I lack the bump of paternity.'

 Johann Kaspar Lavater (1741-1801) was a Swiss mystic poet and physiognomist, famous for reviving the idea that a person's physical appearance sheds light on their personality. Here Prince Vasili seems to be confusing physiognomy with phrenology, the discredited idea that character traits manifest themselves in bumps and dents in the head.