On to Hegel
Having spent most of 9 chapters relentlessly bashing Plato, Popper now turns to praising his originality and profundity. Mostly this praise does not delve too deeply into what is being praised, but a few remarks caught my eye, especially the claim that Euclid was not so much a textbook of geometry as the Platonic schools attempt to provide a foundation for Plato's geometric cosmology, expounded in Timaeus. Since I mainly recall Timaeus as as absurd and naive, I was a bit befuddled by the remark, but one can hardly doubt that even Kepler was long under the spell of Timaeus.
I mostly remembered the dialogue for the central role played by the five Platonic solids, but Wikipedia has a nice summary: https://en.wikipedia.org/wiki/Timaeus_(dialogue)#Synopsis_of_Timaeus'_account, which includes some nicely animated rotating images of those solids.
Next, Popper begins Hegel with a chapter on Aristotle, whom he regards as Hegel's source and inspiration. Popper is not a fan of the Stagirite, who is dismissed as wordy and lacking in originality.
That Hegel will fare worse is foreshadowed by this epigraph to Chapter 11:
The philosophy of Hegel, then, was … a scrutiny of thought so profound that it was for the most part unintelligible … J. H. STIRLING.
Popper, Karl R.. The Open Society and Its Enemies (Princeton Classics) . Princeton University Press. Kindle Edition.