De civilitate morum puerilium libellus

...and to commending those illustrious gifts of the mind to the eyes of men. A person's decorum. It is fitting, however, that a person be entirely composed in mind, body, gestures, and clothing: but it is especially fitting for boys to show all modesty, and in these, particularly for the noble. Nobles. For those are to be considered noble who cultivate their minds with the liberal arts. Let others paint lions, eagles, bulls, and leopards on their shields; those possess more true nobility who can depict as many images for their coat of arms as they have mastered liberal arts.

Therefore, so that a boy's well-composed mind may shine forth in every way (and it shines forth most especially in the face), let the eyes be calm, modest, and composed: not grim, which is a sign of ferocity; not dishonest, which is a sign of impudence; not wandering and rolling, which is a sign of insanity; not squinting, which is a sign of the suspicious and those plotting treachery; nor excessively wide, which is a sign of the stupid; nor constantly closing the eyelids and lashes, which is a sign of the inconstant; nor stupefied, which is a sign of those who are astonished, that which is noted in the astonished Socrates. What is fitting for the eyes. Socrates astonished.