“Hair is fixed to the thin skin of the skull and provided by nature not so much for a useful purpose as for mere ornament.” (DNP 6.17.2)
As William goes on to indicate, however, the presence of hair on the head is more than merely ornamental:
“The human body, because of its heat and moistness, cannot be without vapor. But it is in the nature of vapor to rise. So to prevent all the heat from evaporating, God placed the skull above and covered it with a thin hide of skin. But so that excess matter could escape, He placed certain orifices [the pores] both in the skull and the skin. The thick vapor, therefore, escaping through the narrow pores of the skin, sticks there by its own viscosity and is further thickened by the coldness of the outside air. And because it leaves through a round orifice it takes on a round shape. More vapor follows, which forces out the first and joins itself to it by its own viscosity, and so hair grows in length.” (DNP 6.17.3)
Hair as frozen body vapor. Nice.
“The head is a spherical substance extended by a approximately two inches to the front and behind. The reason why it is a spherical substance is that a human being, for the most dignified organ of this body, should possess the shape of the celestial bodies, for he possesses in his soul a likeness of celestial things through reason and immortality. This was also done by God rather usefully so that the brain might move through the head more easily and any excess matter might not remain in its corners, if it were angular, and corrupt it.” (DNP 6.17.1)
“The wise man always has something to do. During the day he should be using his eyes for reading, his tongue for teaching, his hand for writing; at night his soul, free from the bondage of the body, should use both its rational faculty to descend to the corporeal realm and its intellective faculty to ascent to the incorporeal.” (William of Conches, A Dialogue on Natural Philosophy 2.1.1)
“No philosophical doctrine is so false that it does not have some truth mixed with it…” William of Conches, A Dialogue on Natural Philosophy, 1.6.8)