There's a paucity of further info on Julius Caesar's horse "Toes". You'd think someone would have immortalized him in a fresco or some other artwork, but not so far that I find. Not to mention, wouldn't there have been any other polydactyl horse even a bit like him?
There would. And in the American Journal of Sciences, Third Series Vol. XLIII, No. 256 -- that's April 1892's issue -- O.C. Marsh lays it all out for us in Recent Polydactyle Horses.
It is not light reading.
However, we learn of "Clique, the horse with six feet," who was said to be from Texas, and died at a respectable horse age in 1891, and some "Eight-footed Cuban horse." There is reason to believe that the Mustangs of the American southwest have a connection to the polydactyl tendency. And we hear that tapirs have the most primitive feet of existing perissodactyls (odd-toed ungulates).
Want to try reading it?