Students of the Orestes are fortunate to have two excellent commentaries at their disposal, by C. W. Willink (Oxford, 1986) and M. L. West (Warminster, 1987). Neither will help them to understand this line, which is ‘the only allusion to Ganymede's horsemanship’ (Willink ad loc), because ‘no story of riding by Ganymede is known’ (West ad loc). But we are repeatedly reminded that the scene with the Phrygian (1369ff.) has far fewer affinities with tragedy than with comedy, and εύριπιδαριστοφαíζεται Comedy provides the clue, specifically at Ar. Vesp. 50If. and Lys. 676ff. The reference is to the variety of equestrianism for which Ganymede is far from unknown (he was too young to have established an association with any other kind). For Innoavvr) here describes a σχῆμα ἐρωτικóν and the line means Ganymedes concubinus, Iovis supini inguini insidens et equitans, sc. inter causas fuit malorum propter Iunonis invidiam Troianis immissorum.