the pincheed area's arent actually together there is a gap between the sides so that it can come out its just there to keep the closure in the neck, the closure was a marble that seals against a rubber ring the carbonation kept the pressure on the marble so that it wouldnt fall and stayed sealed
In answer to bottlenutboy's comment in regard to Australian Codds or "Marble Bottles", each state of Australia produced its own brands of bottles in up to ten different Codd patent types.
At a very rough guess, I would have to say that there are quite possibly over 10,000 different varietis from all of the companies known. Victoria and New South Wales had more brands and varieties than most of the other states.
There is an Australian bottle forum that you are welcome to look at for more information.