“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.