Corpus Christi is a Double of the First Class with a privileged Octave of the Second Order.
Celebration of the feast began with First Vespers yesterday afternoon. The antiphons Sacerdos in aeternum etc were sung with psalms 109, 110, 115, 127 & 147. The chapter, hymn, versicle and response, antiphon on the Magnificat and collect are all proper feast. There were no commemoration. At Compline Te lucis was sung with the melody and Doxology of the Incarnation, Jesu tibi sit gloria, Qui natus es de Virgine, Cum Patre et almo Spiritu, In sempiterna saecula.
At Mattins the invitatory is Christum Regem adoremus dominantem Gentibus: Qui se manducantibus dat spiritus pinguedinem. The Office hymn is Sacris solemnis. The antiphons and psalms are proper at each of the nocturns. In the first nocturn the lessons are taken from the First Epistle of St. Paul to the Corinthians. In the second nocturn the lessons are taken from the writings of St. Thomas Aquinas and the homily in the third nocturn is from St. Augustine on St. John's Gospel. At Lauds the antiphons, a different set to those sung at Vespers, are proper, Sapientia etc. These are sung with the Dominical psalms. The Office hymn is Verbum supernum.
At the Hours the antiphons from Laudes are sung with the festal psalms. The Office hymns are sung with the melody and Doxology of the Incarnation. At Prime (Pss. 53, 118i & 118ii) the versicle Qui natus es is inserted into the short responsory and the lectio brevis is Quicumque manducaverit panem etc.
The Mass, Cibavit eos, is sung after Terce. The Gloria is sung, the Sequence Lauda Sion is sung, the Creed is sung and the preface is of the Nativity. Two large altar breads are placed on the corporal and consecrated. After the consecration the rubrics for Mass coram Sanctissimo are followed, with the celebrant not turning his back on the altar. Ite, missa est, the blessing and last Gospel are said as normal. After Mass the celebrant exchanges his chausuble for a cope and a Procession takes place. The Caermoniale Episcoporum gives detailed instructions for the Procession (indeed so detailed they forsee the bishop having to excommunicate persons who cannot agree their respective position in procession!) It also sanctions the practice of Mass and Vespers coram Sanctissimo during the Octave.
At Second Vespers all is at First Vespers except the antiphon on the Magnificat which is proper. A commemoration is sung of St. Francis Caracciolo.
In the 'liturgical books of 1962' the hymns of the Hours do not have their Doxology changed in honour of the Incarnation. At Prime the versicle is of the season, not of the Incarnation, and the chapter is of the season too. At Mass the common preface is sung. When a Procession takes place Benedicamus Domino is sung instead of Ite, missa est, the blessing and last Gospel are omitted. At Second Vespers there is no commemoration. The Octave has been abolished.