De civilitate morum puerilium libellus

to scratch the head in front of others is not very decorous, just as it is sordid to rub the rest of the body with your fingernails, especially if it is done by habit and not by necessity. The hair should neither cover the forehead nor float about the shoulders. To shake the hair by tossing the head from time to time is the act of frolicking horses. To pull the hair back from the forehead to the crown of the head is not very elegant: to part it with the hand is more modest.

The neck.

To bend the neck and shrug the shoulders argues for laziness: to arch the body backward is a sign of pride; it is proper to be softly erect. The neck should not veer to the left or right: for that is hypocritical, unless conversation or something similar demands it.

The shoulders.

It is necessary to balance the shoulders with an equal poise, not to lift one and depress the other in the manner of antennae. For gestures of this kind, when neglected in boys, turn into nature and deform the carriage of the body in a way that is contrary to nature.

From the resulting inconvenience.

Therefore, those who have collected the habit of slouching acquire for themselves a hunched back which nature had not given; and those who have become accustomed to having the head bent to the side...