What the author is saying in this text is that the sculptures are so precise that they are still impressive when you look at them up close, even though they were not meant to be exhibited directly on the floor, but on a high pedestal. The "jowls" and "muzzle" of the horse are the "things that could not have been seen when they were on their high perch," yet the carver paid as much attention to detail ("cut with as much care") when he sculpted them as if they were at eye level ("as though they had been made for the floor").
