The Riksdag underwent profound changes in 1867, when the medieval Riksdag of the Estates was abolished. The new form of the Riksdag included two elected chambers, each with its own speaker. Since the "de facto" introduction of parliamentarism in 1917, the Riksdag has properly functioned as the institution to which the Prime Minister and the Government are held accountable. In 1971 the institution was transformed into a unicameral legislature with 350 members, reduced to 349 in 1976 to avoid parliamentary deadlocks. Since 1975, in accordance with the Instrument of Government of 1974, it is the speaker and no longer the Monarch who appoints and dismisses the Prime Minister.