I class with a II class octave
Midnight Mass: The Midnight Mass, as given in the Missal, may not begin before midnight. The faithful may receive Holy Communion at only one of the three Masses of Christmas.
An image of the Christ Child should be visible in the sanctuary during Christmastide; it is incensed in the same manner as the altar cross.
There are three proper Masses: Midnight, Dawn, and Day. Priests may celebrate all three. The Midnight Mass follows Matins, the Dawn Mass follows Prime, and the Day Mass follows Terce.
At each Mass: Credo, Preface of the Nativity, and proper Communicantes for the entire octave.
In the Communicantes in the Midnight Mass, say Noctem sacratissimam celebrantes, qua, in place of the words Diem sacratissimum celebrantes, quo, which is used for all other Masses of the Feast and Octave. In the second Mass (even solemn) commemorate St. Anastasia (Martyr). At the end of the third Mass, omit the Last Gospel.
Regarding the particular ceremonies involved when two or three Masses are celebrated within a short time frame, see the rubrics of Trination. When one Mass follows another without pause, the prayers after Low Mass are omitted, to be said only after the final Mass of the series.
In Sung Masses the ministers genuflect at the words Et incarnatus est when they are recited, then kneel when they are sung, even if the ministers are already at the sedilia (they kneel there).
There is no commemoration of St. Anastasia in the Office.
Matins: Invitatorium Christus natus est; Hymn Iesu, Redemptor; 3 Nocturns all proper; Te Deum
Lauds: Proper antiphons with Sunday psalms of the 1st scheme; Hymn A solis ortus
Prime: Psalm 53 instead of 117 (ut in festis); in short responsory, versicle Qui natus es is said and short lesson Ipsi peribunt
Hours: Sunday psalms with antiphons from Lauds
II Vespers: Of the Nativity, proper
Compline: Of Sunday