I added the below image and caption to the Trombone History Timeline (17th century—2nd half). This portrayal of a trombone is a little unusual, but it does reflect the general shape of the instrument.
1679—Certosa di Pavia, Italy: A fresco by Giuseppe Procaccini includes an angel playing what appears to be a trombone. Although the rear bow of tubing does not extend behind the player’s head as it should, the instrument appears to have a slide and the general configuration of a trombone (see detail and full image below; public domain). Click to expand.