Mizzentopmast

If this cannot be done, brace the crossjack-yards to the wind, and, if necessary, send down the mizzentopmast and the crossjack-yard.

Source: wiktionary

Without fear Mrs. Weldon saw Jack, in company with Dick Sand, spring out on the shrouds, climb to the top of the mizzenmast, or to the booms of the mizzentopmast, and come down again like an arrow the whole length of the backstays.

Source: wiktionary