timaeus   

opposite of the truth; and they become false and foolish, and there is
no course or revolution in them which has a guiding or directing
power; and if again any sensations enter in violently from without and
drag after them the whole vessel of the soul, then the courses of
the soul, though they seem to conquer, are really conquered.
And by reason of all these affections, the soul, when encased in a
mortal body, now, as in the beginning, is at first without
intelligence; but when the flood of growth and nutriment abates, and
the courses of the soul, calming down, go their own way and become
steadier as time goes on, then the several circles return to their
natural form, and their revolutions are corrected, and they call the
same and the other by their right names, and make the possessor of
them to become a rational being. And if these combine in him with
any true nurture or education, he attains the fulness and health of
the perfect man, and escapes the worst disease of all; but if he
neglects education he walks lame to the end of his life, and returns
imperfect and good for nothing to the world below. This, however, is a
later stage; at present we must treat more exactly the subject
before us, which involves a preliminary enquiry into the generation of
the body and its members, and as to how the soul was created-for
what reason and by what providence of the gods; and holding fast to
probability, we must pursue our way.
First, then, the gods, imitating the spherical shape of the
universe, enclosed the two divine courses in a spherical body, that,
namely, which we now term the head, being the most divine part of us
and the lord of all that is in us: to this the gods, when they put
together the body, gave all the other members to be servants,
considering that it partook of every sort of motion. In order then
that it might not tumble about among the high and deep places of the
earth, but might be able to get over the one and out of the other,
they provided the body to be its vehicle and means of locomotion;
which consequently had length and was furnished with four limbs
extended and flexible; these God contrived to be instruments of
locomotion with which it might take hold and find support, and so be
able to pass through all places, carrying on high the dwelling-place
of the most sacred and divine part of us. Such was the origin of
legs and hands, which for this reason were attached to every man;
and the gods, deeming the front part of man to be more honourable
and more fit to command than the hinder part, made us to move mostly
in a forward direction. Wherefore man must needs have his front part
unlike and distinguished from the rest of his body.
And so in the vessel of the head, they first of all put a face in
which they inserted organs to minister in all things to the providence
of the soul, and they appointed this part, which has authority, to
be by nature the part which is in front. And of the organs they
first contrived the eyes to give light, and the principle according to
which they were inserted was as follows: So much of fire as would
not burn, but gave a gentle light, they formed into a substance akin
to the light of every-day life; and the pure fire which is within us
and related thereto they made to flow through the eyes in a stream
smooth and dense, compressing the whole eye, and especially the centre
part, so that it kept out everything of a coarser nature, and
allowed to pass only this pure element. When the light of day
surrounds the stream of vision, then like falls upon like, and they
coalesce, and one body is formed by natural affinity in the line of
vision, wherever the light that falls from within meets with an
external object. And the whole stream of vision, being similarly
affected in virtue of similarity, diffuses the motions of what it
touches or what touches it over the whole body, until they reach the
soul, causing that perception which we call sight. But when night
comes on and the external and kindred fire departs, then the stream of
vision is cut off; for going forth to an unlike element it is
changed and extinguished, being no longer of one nature with the
surrounding atmosphere which is now deprived of fire: and so the eye