Ember Saturday in Advent is a greater, non-privileged, ferial day of simple rite and its liturgical colour is violet. The Vigil of St. Thomas the Apostle is commemorated at Mass only. Today is one of the traditional days for ordinations.
At Mattins the invitatory Prope est jam Dominus etc is sung and the Office hymn is Verbum supernum prodiens. In the nocturn the antiphons Memor fuit etc are sung with the nine psalms appointed for Saturday 104, 105 and 106 - each split into three divisi. The three lessons are from a homily of St. Gregory on St. Luke's Gospel. After the third responsory, Veni, Domine, et noli tardare etc., the second scheme of Lauds for Saturday is sung. The special set of antiphons for the Saturday before the Vigil of the Nativity, Intuemini etc., are sung with psalms 50, 91, 63, the Canticle of Moses & 150. The Office hymn is En clara vox. The antiphon on the Benedictus is Quomodo fiet istud etc. After the antiphon is sung in full after the canticle the choir kneels and the ferial preces are sung. The collect is proper to the Ember Saturday, Deus qui conspicis.
At the Hours the antiphons Intuemini etc are used in the usual sequence. At Prime (Pss 93i, 93ii, 107 & 149. The fourth psalm is the one displaced by the Miserere in the second schema of Lauds. The chapter is the ferial Pacem et veritatem. The Dominical and ferial preces are sung with the choir kneeling. At the other Hours the short set of ferial preces are sung, again with the choir kneeling.
Mass is sung after None and has the usual, ancient, form, common to Ember Saturdays. The ministers wear folded chasubles. After the Kyrie there are a series of five structural units comprising of the invitation Oremus, followed by Flectamus genua (sung by the deacon), Levate (sung by the sub-deacon), a collect, O.T. reading and gradual. Four of these readings are from Isaiah and the last from Daniel. After the pericope from Daniel instead of a gradual the hymn of the Three Men in fiery furnace is sung, Benedictus es, Domine, Deus patrum nostrorum and its collect Deus, qui tribus pueris. After this collect the second collect is of the Vigil of St. Thomas and the third collect is of the BVM, Deus, qui de Beate. Mass then continues as usual (with of course kneeling for the orations and from the Canon through to the Fraction as usual on penitential days) with Benedicamus Domino, sung as the dismissal by the deacon facing the altar, and the last Gospel is of the Vigil of St. Thomas. Private Masses may be of the Vigil of St. Thomas. When ministers are present they wear dalmatic and tunicle, not plantis plicatis. In the Mass of the Vigil the second collect is of the Ember Saturday (the collect after the Kyrie, Deus, qui conspicis), the third collect is Deus, qui de Beate, Benedicamus Domino is the dismissal and the last Gospel is of the Ember Saturday.
In the afternoon Vespers of the fourth Sunday in Advent are sung. The antiphons Canite tuba etc are sung with the Saturday psalms. The Office hymn is Creator alme siderum and the Great 'O' Antiphon O clavis David is sung. The 'Great O' Antiphons are 'doubled', i.e. they are sung entire both before and after the Magnificat even on days of simple rank with the choir standing. At Compline the Dominical preces are sung (the choir standing).
Following the 'liturgical books of 1962' the Vigil of St. Thomas has been abolished. At Lauds the Canticle of Moses gets sliced down from 65 to 27 verses. At Prime the fourth psalm is not added and the ferial chapter Pacem et veritatem is replaced by the festal Regi saeculorum. The ferial preces are omitted at Prime and the Hours. The Mass has the option of the 'mini-Ember Day' consisting of just one additional unit of collect, pericope and gradual. There are no additional collects for St. Thomas or the Blessed Virgin. The ministers wear dalmatic and tunicle, the dismissal is Ite, missa est and the last Gospel is In principio. The doubling of the Great 'O' Antiphons is no different to all other antiphons throughout the year. The Dominical preces are omitted at Compline.