These photographs are from the collection of Whelden Merritt, as is the explanatory text.
This is very rare, it is a Bavarian post horn with valves. Here is a picture of it being played by a Bavarian Postillion. In C with an A crook – the notes must be lipped into proper intonation. There is virtually no room for adjustment of the semitone valve slide.
Bavarian Postillions were not issued valved instruments as service instruments. They must be played with both hands and that lead to many accidents, especially in Prussia where entire post coaches full of passengers landed in the ditch because the driver was using both hands to play his valved post horn. The Postillions earned tip money by entertaining people with their post horns, so the temptation was great to get carried away with variations on the Carnival of Venice or some such. The King of Bavaria did not want to be as foolish as his old rivals, the Prussians, so he appointed a commission which came up with a compromise solution – a one-handed post horn with one finger hole that allowed CERTAIN diatonic melodies to be played, including the national anthem. This was issued to the Postillions as a service instrument.