Today is the third day within the Octave of the Epiphany, it is of semi-double rite, as are all days within the Octave except the Octave Day which is greater double.
Yesterday at Mattins the normal structure was resumed with the opening verse Domine, labia, invitatory and hymn. The antiphons and psalmody is as on the feast except in the third nocturn the psalm Fundamenta replaces the special arrangement of psalm 94. (The antiphons, of course, are not doubled on a semi-double day.) Scripture is taken from St. Paul's letter to the Romans. Mattins has nine lessons.
At Lauds the antiphon on the Benedictus is proper for each day. At the Hours the antiphons and psalmody is as on the feast.
At Mass the Gloria is sung, the second collect is of the BVM, Deus, qui salutis, the third for the Church, Ecclesiae, or the pope. The Credo is sung and the preface and communicantes are as on the feast. Vespers are of the Octave with the antiphon on the Magnificat being proper to each day. Compline is festal.
In the 'liturgical books of 1962' the days after the Epiphany become IV class ferial days of Epiphanytide. Mattins has one nocturn and the psalmody is ferial. At the Hours the hymns do not have the Doxology in honour of the Epiphany and again have ferial psalmody. Despite the ferial psalmody the antiphons are doubled. At Mass the Gloria is sung, the additional collects and Credo are omitted. Vespers has ferial psalmody as does Compline.