Doors and windows usually terminate in a horizontal line at top. These require no special directions for their trimmings. But circular-headed doors and windows are more difficult of execution, and require some attention. If the jambs of a door or window be placed at right angles to the face of the wall, the edges of the soffit, or surface of the head, would be straight, and its length be found by getting the stretch-out of the circle (Art. 524); but when the jambs are placed obliquely to the face of the Avail, occasioned by the demand for light in an oblique direction, the form of the soffit will be obtained by the following article; as also when the face of the wall is circular, as shown in the succeeding figure.