Source:
http://www.oddmusic.com/gallery/om24750.html
The serpent is a large bass wind instrument designed for the lower pitches, and thus similar in function than the modern tuba. Serpents typically have two sets of three fingerholes that are used to change the length of the pipe.
They are typically made of wood, covered with leather. The mouthpiece is similar to that of the bugle and trumpet, where the vibrating lips cause the Bernoulli effect.
Source:
http://www.oddmusic.com/gallery/om24750.html
Source: http://en.wikipedia.org/wiki/File:Serpent_groves.jpg
It is unclear when the serpent was invented, although one tradition traces it back to Edmé Guillaume in 1590 in Auxerre (France). The instrument was played until the 1800s, when it was replaced by the ophicleide which offered more control by having more keys.
http://en.wikipedia.org/wiki/File:Serpent_recording_2.ogg
http://www.serpentwebsite.com/sound.htm