I just added the below image and caption to the Trombone History Timeline (19th century: 1826-1850) and to the collection of rear-facing trombone images, Backward Advances: Rear-Facing Trombones throughout History.

c. 1828—Paris, France: Frédéric Bouchot’s La Grisette abandonée, No. 2, second in a series of seven lithographs, includes a rear facing trombone in the music ensemble (see below image; public domain).