μετάφρενον · metaphrenon — LSJ
part behind the midriff (μετὰ τὰς φρένας), broad of the back: hence, generally, back, μεταφρένῳ ἐν δόρυ πῆξεν ὤμων μεσσηγύς Il. 5.40, cf. 56, al.; μ. ἠδὲ καὶ ὤμω πλῆξεν 2.265; μ. ἠδὲ καὶ ὤμους (of a woman) Od. 8.528, cf. Hp. Acut. 66; in pl., of a single person, Il. 12.428; ὤμους καὶ μετάφρενα, of a woman, Archil. 29. cf. Hld. 10.32. — Ep. word, used by Pl. Prt. 352a, Arist. Phgn. 810b25, Luc. DMeretr. 4.2.
= τὸ μεταξὺ τοῦ νώτου καὶ ὀσφύος κατὰ τὴν τῶν φρενῶν πρόσφυσιν Ruf. Onom. 90.