Columbia subject headings:
Catholic Church. Gradual (Pre-Vatican II)--History--Sources.
Mass (Music)--History--Sources.
Harvard subject headings:
Catholic Church--Italy--Rome--Liturgy--Manuscripts.
Catholic Church--Italy--Rome--Liturgy--Texts.
Gregorian chants--Manuscripts.
Princeton subject headings:
Catholic Church. Gradual--History--Sources.
Mass (Music)--History--Sources.