I don't read that as counting the prayer over the offerings among the dialogues. I think it refers to the prayer itself, which was historically said inaudibly even at Sung Masses, not the Orate fratres/Pray, brethren - Suscipiat/May the Lord accept, although there is notation for that dialogue in the current English edition of the Roman Missal as well as the Graduale Novum, using the same tone with recitation on la dropping down to sol for a few syllables.In the Eucharistic Liturgy: the prayer over the offerings; the preface with its dialogue and the Sanctus; the final doxology of the Canon, the Lord's prayer with its introduction and embolism; the Pax Domini; the prayer after the Communion; the formulas of dismissal.
One doesn't sing Orate, fratres so the likelihood of that having music is (while not impossible) remote.
A reading from the holy Gospel according to N,
Glory to you, O Lord.
&
The Gospel of the Lord.
Praise to you Lord Jesus Christ.
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