Whipple-tree

At the back of the whipple-tree there are two "revolving shafts," extending from near the middle to the ends; the ends of these shafts are bent at right angles, and they are so arranged that the outer end of each one, which is flattened for that purpose, covers the end of the pin on the whipple-tree, to prevent the traces from flying off; and to the inner ends a cord is attached, to enable the driver to turn the shafts, and thus uncover the ends of the pins, and permit the traces to escape.

The pivoted front axle for wagons was known to the Romans and continued in use; but horses, with their swift and abrupt motions, could not safely be attached to a heavy load until the whipple-tree was invented.

The advantage of the curved beam and whipple-tree is that it can be used to harness almost any number of animals.