Ma bouche rit
Anonymous:
Kyrie   Gloria   Credo   Sanctus   Agnus Dei
Source: VienNB 11883, fols. 285v-294r.
I am most grateful to Kara Olive (Princeton University) for allowing me to use her transcription of this Mass.

Malheur me bat
Alexander Agricola:
Kyrie   Gloria   Credo   Sanctus   Agnus Dei
Edition: Alexander Agricola, Opera omnia, ed. Edward R. Lerner, 5 vols., Corpus mensurabilis musicae, 22 ([s.l.:] American Institute of Musicology, 1961-1970), 1: 66-104.
The opening of Agricola’s Credo, which is based on the plainchant Credo I, seems to allude to the opening of the Credo of Compère’s Missa L’homme armé.
Josquin des Prez:
Kyrie   Gloria   Credo   Sanctus   Agnus Dei
Edition: Josquin des Prez, The Collected Works (“New Josquin Edition”), gen.ed. Willem Elders, 30 vols. (Utrecht: Koninklijke Vereniging voor Nederlandse Muziekgeschiedenis, 1987- ), 9: 1-42.
Jacob Obrecht:
Kyrie   Gloria   Credo   Sanctus   Agnus Dei
Edition:  Jacob Obrecht, New Obrecht Edition, gen.ed. C. J. Maas, 18 vols. (Utrecht: Vereniging voor Nederlandse Muziekgeschiedenis, 1983-1999), 7: 1-37.

Ma maistresse
Johannes Ockeghem:
Kyrie   Gloria
Source: Johannes Ockeghem, Collected Works, ed. Dragan Plamenac, 3 vols. (Philadelphia, Pa.: American Musicological Society, 1947-1992), 1: 117-123.

Maria mater ad me venit
Paullet Macarne:
Kyrie   Gloria
Source:  LiverC Fab. 4, fols. 20v-29r.
This little-known choirbook also contains a fragmentary five-part motet Ego flos campi by the otherwise unknown composer Johannes Le Non. The unidentified cantus firmus bears the incipit campi fragorum, and enters at 0:49, where it coincides with the word “campi” in the other voices. The tune appears to be of secular origin; perhaps it is related to the anonymous Goliard song Deveham te in campos fragorum. I have recorded only the beginning of the prima pars.
Update (Sept. 2008): newly-uncovered fragments dated c.1380, in the Gemeentelijk Archief Duivenvoort (Netherlands), have yielded a hitherto-unknown song based on the very same cantus firmus, the four-part Laisse moy t’emmener (click here for a modern edition) by Magister Joris Henricxzone, who was evidently a follower of Machaut.

Maria zart
Anonymous:
Kyrie   Gloria   Credo   Sanctus
Edition: Thomas L. Noblitt, ed., Der Kodex des Magister Nicolaus Leopold: Staatsbibliothek München Mus. ms. 3154, 4 vols., Das Erbe deutscher Musik, 80-83 (Kassel and New York: Bärenreiter, 1987- ), 3: 265-75.
Jacob Obrecht:
Kyrie   Gloria   Credo   Sanctus   Agnus Dei
Edition: Jacob Obrecht, New Obrecht Edition, gen.ed. C. J. Maas, 18 vols. (Utrecht: Vereniging voor Nederlandse Muziekgeschiedenis, 1983-1999), 7: 39-96.

Mater Patris
Josquin des Prez:
Kyrie   Gloria   Credo   Sanctus   Agnus Dei
Edition:  Josquin des Prez, Werken, ed. Albert Smijers, (Amsterdam: Vereniging voor Nederlandse Muziekgeschiedenis, 1927-69), I. iii. 1-31 (Aflevering 26, Missen 12).

Meditatio cordis
Anonymous:
Gloria   Credo   Sanctus   Agnus Dei   Motet
Sources: PragP 47, fols. 85v-92r (Mass); TrentC 88, fols. 284v-286r (motet Gaude Maria; c.1460-62).
Edition used here:  Robert J. Snow, “The Manuscript Strahov D.G.IV.47” (Ph.D. diss., University of Illinois, 1968), 277-315.

Mi mi
Johannes Ockeghem:
Kyrie   Gloria   Credo   Sanctus   Agnus Dei
Edition: Johannes Ockeghem, Collected Works, ed. Dragan Plamenac, 3 vols. (Philadelphia, Pa.: American Musicological Society, 1947-1992), 2: 1-20.

Mon cuer pleure
Guillaume le Rouge (lost):
Mentioned in Johannes Tinctoris, Proportionale musices (c.1472-73); see Tinctoris, Opera theoretica, ed. Albert Seay, 2 vols., Corpus Scriptorum de Musica, 22 (American Institute of Musicology, 1975-78), 2a: 47.

Mon oeuil est de tendre tempure
Johannes Tourout:
Kyrie   Gloria   Credo   Sanctus   Agnus Dei
Source: TrentC 89, fols. 258r-273r (c.1460-62).
For the Mass and its model, see Adelyn Peck Leverett, “Song Masses in the Trent Codices: The Austrian Connection,” Early Music History, 14 (1995): 205–56, at 237-44.
NB. The double leading tone at Gloria 7:30 is indicated in the source.

Moro perche non hai fede
Guillaume Garnier (lost).
Mentioned by Franchinus Gaffurius in Tractatus practicabilium proportionum (c.1482). See Clement A. Miller, “Early Gaffuriana: New Answers to Old Questions,” Musical Quarterly, 56 (1970): 367-88, at 379.