Although it looks like a fantasy instrument that might have been designed to accompany vacuum cleaners in a Gerard Hoffnung music festival, the serpent is a bona fide wind instrument, with a pedigree dating back over four centuries.
The Serpent is an ancient musical wind instrument, related to the modern Tuba, Euphonium, and Baritone (see Pictures). It is blown with a cup shaped mouthpiece which is very similar to that of a trombone or Euphonium/Baritone. Played softly, it has a firm yet mellow tone color, or timbre. At medium volume, it produces a robust sound which seems to be a cross between the tuba, the bassoon, and the French horn. When played loudly it can produce unpleasant noises reminiscent of large animals in distress...
Many observers are confused in their efforts to classify the Serpent. The use of wooden construction with finger holes does not mean that the Serpent is a woodwind instrument! Because the sound originates with the vibration of the player's lips in a cup mouthpiece, the Serpent is classified as a brass instrument...
The shape results from the need to bring the finger holes within reach of the player, on what is actually a rather large instrument.
Further (extensive) information is available at The Serpent Website.
Link. Photo via Sublime Things.
Nice to see a picture of it.
The serpent is a very difficult instrument to play in tune. The tone holes don't really have as much effect as embouchure. Most early "brass" ensembles prefer to use sackbutts.