Note that even a full-rigged ship did not usually have a lateral (square) course on the mizzen mast below the mizzen topmast. Instead, the lowest sail on the mizzen was usually a fore/aft sail—originally a lateen sail, but later a gaff sail called a spanker or driver. The key distinction between a "ship" and "barque" (in modern usage) is that a "ship" carries a square-rigged mizzen topsail (and therefore that its mizzen mast has a topsail yard and a cross-jack yard) whereas the mizzen mast of a barque has only fore-and-aft rigged sails. The cross-jack yard was the lowest yard on a ship's mizzen mast. Unlike the corresponding yards on the fore and main mast it did not usually have fittings to hang a sail from: its purpose was to control the lower edge of the topsail. In the rare case that the cross-jack yard did carry a square sail, this sail would be called the cross-jack rather than the mizzen course.