ὥσπερ γὰρ οἰκίας οὐδὲν ὄφελος ἂν εἴη, εἰ τὰ ἄνω πάνυ καλὰ ἔχοι μὴ ὑποκειμένων οἵων δεῖ θεμελίων, οὕτω καὶ ἵππου πολεμιστηρίου οὐδὲν ἂν ὄφελος εἴη, οὐδ᾽ εἰ τἆλλα πάντα ἀγαθὰ ἔχοι, κακόπους δ᾽ εἴη: οὐδενὶ γὰρ ἂν δύναιτο τῶν ἀγαθῶν χρῆσθαι.
I am having much difficulty with the beginning of this sentence from Xenophon.
οἰκίας: is this accusative of respect?
τὰ ἄνω: is this an adverb used to make a substantive? "the upward parts"?
ὑποκειμένων: is this an absolute genitive?
θεμελίων: what part of speech is this?
I am really not interested in the rest of the sentence, but if someone can give me a complete gloss for the bold I would be much obliged. I am especially interested in whether various neuter words are subjects or objects, adjectives or substantives. And I am especially interested in an words that are implicit, but not explicit.
Thanks in advance.