A correspondent writes: 'Can you confirm/deny that 'an' used to be 'a' nother etc? If I am right, when did the n migrate?'
I can certainly confirm that a nother existed in English, from around 1300, as a variant of an other. Chaucer has an example: 'And saw a nothere ladye'. It was definitely a variant: there are earlier examples of both an other and another. Interestingly, the Oxford English Dictionary also gives examples of no nother, no notherways (i.e. 'no otherwise'), and the notheren (i.e. 'the others').
The usage stayed a long time in English. It isn't surprising to see it at a time when spelling conventions had not been established, and people wrote more or less as they spoke. But the OED has found an example from as late as 1782, in a Lincolnshire glossary, suggesting that this word division stayed in people's minds, at least in some dialects. In jocular use, I still hear similar usages today: 'Got a napple?' - and you see this kind of thing written sometimes in representations of regional dialect. That people still play with article word-division is shown, in reverse, by graffiti of the type 'Be alert. This country needs lerts.'