National Australia Bank says it has appointed Ken Henry, the former head of the Australian Treasury, to its board.Henry will join the NAB board from November 1, the bank said.Henry retired as secretary of the Treasury in March 2011. He will remain an adviser to he Government.Two other former financial regulators serve on bank boards.Ted Evans, also a former secretary of the Treasury, and now chair of Westpac, joined the bank board in 2001, the same year he left Treasury.Ian MacFarlane, former governor of the Reserve Bank of Australia, serves on the board of ANZ. Macfarlane joined the board of the bank less than six months after leaving the RBA.