Complex sentence: A third row of extra notes was eventually added, loosely derived from the C scale, consisting of accidentals and notes which already existed in the diatonic rows but in opposite bisonoric orientation to make additional chords possible and certain melodic passages easier.
Split into simpler sentences: A third row of extra notes was eventually added, loosely derived from the C scale. These added accidentals and notes that already existed in the diatonic rows, but in opposite bisonoric orientation, to make additional chords possible and certain melodic passages easier.