E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A flat gravestone, a stone coffin or sarcophagus, also a bond stone which extends over the entire thickness of a wall. In architecture, called Perpent or Perpend Stones or Throughs. (French, Pierre parpainge.)
Od! he is not stirring yet, mair than he were a through-stane.Sir W. Scott: The Monastery (Introduction).