NoDictionaries   Text notes for  
... superasset equorum, ni rota, perpetuum qua circumvertitur axem, stipitis...

'perpetuum qua circumvertitur axem' - the clause causes some problems; 'perpetuum' with 'axem'; qua circumvertitur = through which it turns ; what is the subject of 'circumvertitur'? Understand this clause as follows : 'though which (the wheel) the axis turns '; we read litterally 'through which it turns' ; after that the accusative follows, to explain, what then is turning? Well, axem perpetuum! The axis! I believe such an acc. is called a 'respectus'. I am not sure, if this is common, fluent Latin or that Ovid is twisting a bit here with the language. He needs this acc. anyway to make good for the metre here.