Timaeus

I'll keep this discussion very short.  Timaeus relates a long semi-mythical story told by its namesake that describes the creation and structure of the universe.  The story encompasses everything from the demiurge who created the whole world in the image of the one true Living Thing, all the way down to the triangular parts used to construct human organs and provide an account of their operation.  In between, we get the creation of the gods and the heavens and the elements and such.  In other words, it's encyclopedic.  

Obviously, like any creation myth, the interesting thing to ask is not how accurate it is, but how it reveals the values of the author.  Here though, the details pretty boring, because they are exactly the things you would expect from Plato.  Identity is better than difference.  Stasis is better than change.  Soul is better than body.  Rotation is cool because it's the movement that most closely approximates non-movement.  No surprises here.  Perhaps the one thing that is interesting to note is the peculiar separation or reboot of the story that occurs midway through.

Now in all but a brief part of the discourse I have just completed I have presented what has been crafted by Intellect. But I need to match this account by providing a comparable one concerning the things that have come about by Necessity. For this ordered world is of mixed birth: it is the offspring of a union of Necessity and Intellect. Intellect prevailed over Necessity by persuading it to direct most of the things that come to be toward what is best, and the result of this subjugation of Necessity to wise persuasion was the initial formation of this universe. So if I'm to tell the story of how it really came to be in this way, I'd also have to introduce the character of the Straying Cause—how it is its nature to set things adrift.  I shall have to retrace my steps, then, and, armed with a second starting point that also applies to these same things, I must go back once again to the beginning and start my present inquiry from there, just as I did with my earlier one. (48a-b)

This break cannot help but remind us of the way that the myth of the divine shepherd in the Statesman both constituted and contained a reversal between the top down and bottom up aspects of the dialectic.  In one direction, the turning of the world is divinely guided and tends towards order and purity.  Then, like a wind up toy that's been released, it re-turns towards disorder and mixture under its own power.  Something similar seems to be going on here.  The story begins by describing the harmony of the spheres, the way the heavens are ordered by an elaborate system of proportions that reveals the final goals of the Intelligence that created them.  After the break, the story continues by describing the way the universe functions mechanistically.  Timaeus describes a sort of geometrical atomism where everything is composed of triangles.  These triangles interact according to certain laws to produce the intermediate elements of fire, earth, water, and air, and these then combine into sense objects including human bodies.  One side of the story moves backwards from the final purpose, the other forwards from the means used to achieve it.  So in a sense, even this creation myth is dialectical, despite the fact that there is no argument or discussion here, just one long speech.  

You might expect that this dual approach would give Plato a chance to reflect on the various types of causes, and even begin to develop something like Aristotle's theory of four causes.  And indeed, there are a few passages about the "receptacle of becoming" (50b) and "space" (52b) that move in this direction and appear to break the 'mechanistic cause' into something like its material, formal, and efficient parts.  But these reflections seem tangential to the story and aren't developed into a full theory.  You might also expect that there would need to be some sort of epistemological angle here which accounts for the ability of the giant collection of triangles we call the human body to somehow move the soul to be able to perceive the beautiful proportions of the divine design.  And again, there is some mention that this is a problem (61d) and even a hint that the solution is for our "internal revolutions" to somehow mirror the proportions that govern the rotation of the heavens (90d).  But this opportunity too remains mostly unexplored, and the crucial issue of how body and soul, bottom-up and top-down, can interact un-dealt-with.