The most peculiar aspect of Moses’ appearance in art is the pair of horns that are often shown sprouting from his forehead. They are particularly striking in Honoré’s miniature.
The horns came about because of an ambiguity of the Latin version of Exodus 34, 30. After being addressed by God on top of Mount Sinai and given the Tablets of the Law containing the Ten Commandments, Moses descended to his people in the desert. His face was seen to shine with a divine light. The word cornutam used in the Latin translation of the passage can mean both 'shining' and 'horned'.
So in much medieval and Renaissance art the great Jewish leader is shown with goat-like horns emerging from his forehead – a strangely diabolical-looking attribute for this forerunner of Christ.