Looks like "the cruel horse Bucephalus" had pointy teeth and weird horns on its head, as well as eyes that were too far forward for a horse. In fact, of the five horses I can make out, only one does not have twisty horns on its head. I assume that's Alexander on the "horse" that's breaking its chains. It makes me wonder, when the artist does such a good job portraying the people, how he could get the horses so wrong? Had he never seen a horse? Were horses different back then?