What is "swivel bridge"

Swivel \Swiv"el\, n. [AS. sw[=i]fan to move quickly, to remove; akin to Icel. sveifla to whirl, shake, sv[=i]fa to ramble, to turn. See Swoop, and cf. Swift a reel, Swift, a.]

1. (Mech.) A piece, as a ring or hook, attached to another piece by a pin, in such a manner as to permit rotation about the pin as an axis.

2. (Mil.) A small piece of ordnance, turning on a point or swivel; -- called also swivel gun.
   --Wilhelm.

   Swivel bridge, a kind of drawbridge that turns round on a vertical axis; a swing bridge.

   Swivel hook, a hook connected with the iron strap of a pulley block by a swivel joint, for readily taking the turns out of a tackle.

   Swivel joint, a joint, the two pieces composing which turn round, with respect to each other, on a longitudinal pin or axis, as in a chain, to prevent twisting.