On the Institution of Music (De institutione musica)

This diagram illustrates the "Tetrachord Synemmenon," where the notes are joined to the middle note without a gap.

principal of the principals original: "hypate hypaton"
next-to-principal of the principals original: "parhypate hypaton"
index-finger of the principals original: "lychanos hypaton"
principal of the middle notes original: "hypate meson"
next-to-principal of the middle notes original: "parhypate meson"
index-finger of the middle notes original: "lichanos meson"
middle of the conjunct notes original: "mese sinēmenon"
third of the conjunct notes original: "trite sinēmenon"
next-to-highest of the conjunct notes original: "paranete sinēmenon"
highest of the conjunct notes original: "nete sinēmenon"

But since in this or the aforementioned eleven-stringed endecachord arrangement, the middle note original: "mese"; so named because of its central position in the scale comes too close to the highest note original: "nete" and stands too far apart from the lowest principal notes original: "hypatis", it does not retain its proper central place. Therefore, another single four-note scale tetrachord was joined above the "highest of the disjoined notes" original: "nete diezeugmenon". Because these notes must exceed the high pitch of the previously placed highest notes, that entire group was called the extreme notes original: "hyperboleon", in this manner:

This diagram shows the "Disjunct" and "Extreme" tetrachords, reaching the full range of the classical Greek scale.

principal of the principals
next-to-principal of the principals
index-finger of the principals
principal of the middle notes
next-to-principal of the middle notes
index-finger of the middle notes
middle note original: "Mese"
next-to-middle note original: "Paramese"
third of the disjoined notes original: "Trite diezeugmen̄"
next-to-highest of the disjoined notes original: "Paranete diezeugmen̄"
highest of the disjoined notes original: "Nete diezeugmen̄"
third of the extreme notes original: "Trite hyperboleon"
next-to-highest of the extreme notes original: "Paranete hyperboleon"
highest of the extreme notes original: "Nete hyperboleon"

But because, once again, the middle note original: "mese" was not in a central position but happened to be closer to the lower principal notes original: "hypatis", a single string was added below the principal of the principals, which is called the acquired note original: "proslambanomenos". By some, however, it is called the additional melody note original: "prosmelodos", standing a full tone apart from that which is the principal of the principals.

And this "acquired note" itself sounds an octave original: "diapason"; the first and most perfect consonance higher at the middle note. This same additional melody note sounds a fourth original: "diatesseron" at the index-finger of the principals. That index-finger of the principals original: "licanos hypaton" sounds a fifth original: "diapente" at the middle note, which is the fifth note from it.

Again, the middle note stands a tone apart from the next-to-middle note original: "paramese". This same middle note creates a fifth original: "diapenthe" consonance at the highest of the disjoined notes original: "neten diezeugmenon", and an octave original: "diapason" at the highest of the extreme notes original: "neten hyperboleos". The highest of the disjoined notes creates a fourth original: "diatesseron" consonance at the highest of the extreme notes. Finally, the acquired note original: "proslambanomenos" at the bottom renders a double octave original: "bisdiapason" consonance with the highest of the extreme notes at the top, as shown in the following figure: