ἐπὶ τὰ ἰσχία ἄμφω καθίσαι τὼ ἵππω
From LSJ
οὕτως ἐξ ἐχθρῶν αὐτοκτόνα πέμπετο δῶρα, ἐν χάριτος προφάσει μοῖραν ἔχοντα μόρου → thus mutual gifts that bring death were bestowed by enemies, gifts that brought the lot of death in the name of a favor
bring both the horses on to their haunches
