The author of the pasquinade in question is, I believe, unknown.
I am inclined to think that your correspondents, however deeply they may be versed in "Folk-Lore," are generally not much acquainted with "Horse-Lore." Such, at least, is the opinion that is warranted by the extraordinary nature of the questions (not many in number, it is true) which have been put in relation to that subject, and of the replies that have been given to them. In the case now before us, J. R. has only superficially considered the matter. He takes one out of many definitions "in our dictionaries," and on that takes his stand. He is manifestly in error. The tempting facility of referring all words similar in appearance to the same etymon lies at the root of his mistake; for _restive_, as he will find on more patient investigation, is by our lexicographers (Richardson, for example) classed under a different root from _rest_, used to express _quiescence_, or _repose_. _Restive_, or more properly _restiff_, is equivalent to the French _rétif_, or Italian _restio_; and, as applied to horses, means those which resist the will of their rider. Hence, whether in standing stock still, in running away, in rearing, in plunging, or in kicking, they employ their natural means of defence against the control of the cavalier, and may equally be called _restiff_. In support of this view, take the following quotation, to which others might be added. It is from Grisone, _Ordini di Cavalcare_, 4to., 1550:
"Se il cavallo è restio, il più delle volte procede per colpa del Cavaliero, per una di questi ragioni. Overo il Cavallo è vile, e di poca forza, e essendo troppo molestato si abandona e avvilisce di sorte che accorando non vuole caminare avante; over è superbo, e gagliardo, e dandogli fatica, egli mancandogli un poco di lena, si prevalerà con salti, e con aggrupparsi, e con altre malignità, ò fara pur questo dal principio che si cavalca, di maniera che se allora conoscerà chi il Cavaliero lo teme, { 615} prenderà tant' animo, che usando molte ribalderie, si fermerà contra la volontà sua; _e di queste due Specie di Restii_ [which J. R. will be pleased to _note_], la peggior è quella che nasce da viltà, e da poca forza."--Folio 92, verso.