That's a really weird thing. Is it too wide to fit through the mouth of the bottle like it looks in the photo? I haven't got a clue what the purpose of that would be but it would have needed to be added in the factory if that's the case.
The stopper can not be removed, but only lifted slightly. The stopper has a "crossbar" piece of wood that appears to be locked by small protruding wooden pieces. I guess if I filled with "spirits" I'd be able to take a sip, but it would be difficult to fill. The maker's mark on the bottom is a small diamond... Diamond Glass Works, Royersford perhaps.