Commemoration of Ember Saturday; St. Thomas takes precedence liturgically
Traditional day of fast and partial abstinence in the USA
Proper Mass; Gloria; commemoration of the feria; Credo; Preface of the Apostles
Matins: Invitatorium Regem Apostolorum Dominum; Hymn Aeterna Christi munera; psalms and antiphons from the Common of the Apostles; Te Deum
Lauds: Antiphons from the Common of an Apostle with Sunday psalms; Hymn Exultet orbis; commemoration of the feria. Nota bene: For the commemoration of the feria, the Benedictus antiphon is proper to December 21 (printed in the proper section after the III Sunday of Advent): Nolite timere * quinta enim die veniet ad vos Dominus noster.
Hours: Ferial psalms and antiphons
I Vespers: Of the IV Sunday of Advent; antiphons and psalms of Saturday; Magnificat antiphon O Oriens (O Antiphons for Advent); no commemoration of St. Thomas
Compline: Of Saturday