Polled

The one on the right is.
Polled, I mean.
That broken area on the sheep-skull marks where the horn would have grown, as in the left skull. Some breeds are naturally hornless, but sometimes a caustic substance was painted on the lamb's head to kill the horn-bud. These are probably 16th century.

Sorry for the pedagogical and, frankly, dull photo, but this has been the only kind of thing I've been looking at....