The obvious solution would be to read 'quem summo [C in fact reads summo] dubium sub pede semper habet'. This would give orbis a standard epithet, as at Tr V viii 7-8 'nec metuis dubio Fortunae stantis in orbe / numen' and Cons ad Liuiam 51-52 'nempe per hos etiam Fortunae iniuria mores / regnat et incerta est hic quoque nixa rota'. In support of the rather more difficult summo ... pede (='toes') Professor R. J. Tarrant cites Sen Suas II 17 'insistens summis digitis ['toes']—sic enim solebat quo grandior fieret', Sen Tro 1090-91 'in cacumine / erecta summos [uar summo] turba librauit pedes', and Met IV 562 'aequora destringunt summis Ismenides alis'; compare as well Met IX 342-43 'in adludentibus undis / summa pedum taloque tenus uestigia tingit'.
A second solution might be to read 'quem dubio summum sub pede semper habet'; the transfer of dubius from orbis to pes seems acceptable enough, and Met IV 134-36 'oraque buxo / pallidiora gerens exhorruit aequoris instar, / quod tremit exigua cum summum stringitur aura' offers a good parallel to summum.
The image of Fortune standing on her wheel occurs elsewhere in Ovid's poems of exile at Tr V viii 7-8 (quoted above) and EP II iii 55-56 'scilicet indignum, iuuenis carissime, ducis / te fieri comitem stantis in orbe deae'.
33. QVOLIBET EST FOLIO ... INCERTIOR. For the proverb, see Otto folium 1; and from Ovid compare Am II xvi 45-46 'uerba puellarum, foliis leuiora caducis, / inrita qua uisum est uentus et unda ferunt', Her V 109-10 'tu leuior foliis tum cum sine pondere suci / mobilibus uentis arida facta uolant', and Fast III 481-82 (Ariadne speaking) 'Bacche leuis leuiorque tuis quae tempora cingunt / frondibus'.
33. QVAVIS INCERTIOR AVRA. Compare Her VI 109-10 'mobilis Aesonide uernaque incertior aura, / cur tua polliciti pondere uerba carent?'. Otto (uentus 1) cites as well Prop II v 11-13 'non ita Carpathiae uariant Aquilonibus undae, / nec dubio nubes uertitur atra Noto, / quam facile irati uerbo mutantur amantes', Her XVIII 185-86 (Leander to Hero) 'cumque minus firmum nil sit quam uentus et unda, / in uentis et aqua spes mea semper erit?', and Calpurnius Ecl III 10 'mobilior uentis o femina!'.
The folium and uentus images of the present line are found together at Prop II ix 33-35 'non sic incerto mutantur flamine Syrtes, / nec folia hiberno tam tremefacta Noto, / quam cito feminea non constat foedus in ira'.
34. PAR ILLI = par illius leuitati. Similar compressions at vi 40 'mollior est animo femina nulla tuo' and commonly.
37-38. Ovid gives four instances of unexpected catastrophe, two from Greek history, two from Roman; the greater importance of the Roman examples is emphasized by their position and by the doubling of the space allotted to each example from two lines to four. There is a similar transition at Prop II vi 19-20 'cur exempla petam Graium? tu criminis auctor / nutritus duro, Romule, lacte lupae'.
The Greek examples may have been a traditional pairing: Croesus and Dionysius are mentioned together at Lucian Gall 23 as notable instances of personal catastrophe.
37. OPVLENTIA CROESI. Croesus as the archetype of wealth also at Tr III vii 41-42 'nempe dat ... Fortuna rapitque, / Irus et est subito qui modo Croesus erat'.