ἡττώμενος: sc. ὅμως αὐτὰ ποιεῖ.
ὑπὸ μὲν ἡδονῆς: sc. ἡττώμενον, τὰ κακὰ, γιγνώσκοντα ὅτι κακά ἐστι, ποιεῖν. Instead of having μέν followed by its correlative, ὑπὸ δὲ ἄλλου λεκτέον, we have, with anacoluthon, ἐκείνῳ δὴ κτἑ.
ὑβριστής: inclined to mockery.
ἐν ὑμῖν: before you as judges. See on 337 b, l. 34.
οὐ γὰρ ἂν κτἑ.: see on 348 d, l. 6. “If the good were equal to the evil, or greater, evidently there would be no error in choosing it.”