the thumb, C ("C fa ut") was the joint at the base of the index finger, and so on, spiraling around the hand counterclockwise past middle C ("C sol fa ut") until the D a ninth above middle C ("D la sol") (the middle joint of the middle finger) and the E above that ("E la") (the back of that joint, the only note on the back of the hand) were reached. The exact position of the notes on the hand occasionally varies from source to source, so it can be argued that no one version is definitive. This device allowed people to visualize where the half steps of the gamut were, and to visualize the interlocking positions of the hexachords (the names of which—ut re mi fa sol la—were taken from the hymn "Ut queant laxis"). The Guidonian hand was reproduced in numerous medieval treatises. Exact notation to the hexachord system can be found in a reproduction of Ameri Practica artis musice (1271), or in the 1784 source Scriptores ecclesiastici de musica sacra potissimum. The hexachord in the Middle Ages The hexachord as a mnemonic device was first described by Guido of Arezzo, in his Epistola de ignoto cantu and the treatise titled Micrologus. It was the most basic pedagogical tool for learning new music in the European Middle Ages, and was often referenced in contemporary musical theory. In each hexachord, all adjacent pitches are a whole tone apart, except for the middle two, which are separated by a semitone. These six pitches are named ut, re, mi, fa, sol, and la, with the semitone between mi and fa. These six names are derived from the first syllable of each half-line of the 8th century hymn "Ut queant laxis". Each hexachord could start on G, C or F and the adjacent table, reading upwards from the bottom, shows the notes in each hexachord for each of three octaves. Reading from left to right could, within certain limits, permit notes within different octaves to be distinguished from each other. Thus, C (modern c) was "C fa ut" (or "Cefaut"), c (modern c′) was "C sol fa ut", and cc (modern c″) was "C sol fa". Since the lowest pitch was designated by the Greek letter Γ (gamma, for 'g'), the pitch was known as "Gamma ut" or "Gamut", a term which came to designate the range of notes available, and