The serpent is the bass wind instrument, descended from the cornett, and a distant ancestor of the tuba, with a mouthpiece like a brass instrument but side holes like a woodwind. It is usually a long cone bent into a snakelike shape, hence the name. The serpent is closely related to the cornett, although it is not part of the cornett family, due to the absence of a thumb hole. It is generally made out of wood, with walnut being a particularly popular choice. The outside is covered with dark brown or black leather. Despite wooden construction and the fact that it has fingerholes rather than valves, it is usually classed as a brass; the Hornbostel-Sachs scheme of musical instrument classification places it alongside trumpets.
The serpent's range varies according to the instrument and the player, but typically covers one from two octaves below middle C to at least half an octave above middle C.
The serpent usually has six holes, which are ordered in two groups of three. On early models, the fingerholes were keyless, like those of a recorder. However, later models added keys as on a clarinet, although they were for additional holes (out of reach of the fingers), while the original holes remained unkeyed, and are covered or uncovered directly by the player's fingers.
While it does not have a rigidly defined fingering system such as other wind instruments employ, the serpent requires an extraordinary amount of effort from the player, who must select the desired pitch with the lips in falset, usually overriding the tone the instrument prefers to sound with any particular fingering. The serpent player also has a unique right-hand finger position, in that the index finger may be further down the tube towards the bell than the other fingers of that hand. In this respect the fingering of the right hand is reversed to that found in all other keyed wind instruments, where the keys and holes controlled by the index fingers are further up towards the mouthpiece than the other fingers. This is because the serpent was originally held vertically, with both of the player's hands oriented palm-down; in this position the right hand fingerings are not reversed in the manner described above. Later, players began to hold the instrument horizontally.