Timaeus

Moreover, it was not possible to leave the head to consist of bare bone only, because of the excessive variations of temperature in either direction, due to the seasons; nor yet was it possible to allow it to be shrouded up, and to become, in consequence, stupid and insensitive owing to its burdensome mass of flesh. Accordingly, of the fleshy substance which was not being fully dried up a larger enveloping film was separated off, forming what is now called skin. And this, having united with itself because of the moisture round the brain and spreading, formed a vesture round about the head; and this was damped by the moisture ascending under the seams and closed down over the crown, being drawn together as it were in a knot; and the seams had all kinds of shapes owing to the force of the soul’s revolutions and of her food, being more in number when these are more in conflict with one another, and less when they are less in conflict. And the Deity kept puncturing all this skin round about with fire; and when the skin was pierced and the moisture flew out through it, all the liquid and heat that was pure went away, but such as was mixed with the substance whereof the skin also was composed was lifted up by the motion and extended far beyond the skin, being of a fineness to match the puncture; but since it was thrust back, because of its slowness, by the external air that surrounded it, it coiled itself round inside and rooted itself under the skin. Such, then, were the processes by which hair grew in the skin, it being a cord-like species akin to the skin but harder and denser owing to the constriction of the cold, whereby each hair as it separated off from the skin was chilled and constricted. Making use, then, of the causes mentioned our Maker fashioned the head shaggy with hair, purposing that, in place of flesh, the hair should serve as a light roofing for the part about the brain for safety’s sake, providing a sufficient shade and screen alike in summer and in winter, while proving no obstacle in the way of easy perception. And at the place in the fingers where sinew and skin and bone were interlaced there was formed a material blended of these three; and this when it was dried off became a single hard skin compounded of them all and whereas these were the auxiliary causes whereby it was fashioned, it was wrought by the greatest of causes, divine Purpose, for the sake of what should come to pass hereafter. For those who were constructing us knew that out of men women should one day spring and all other animals; and they understood, moreover, that many of these creatures would need for many purposes the help of nails; wherefore they impressed upon men at their very birth the rudimentary structure of finger-nails. Upon this account and with these designs they caused skin to grow into hair and nails upon the extremities of the limbs.