The feast of St. Matthias the Apostle is a Double of the Second Class. St. Matthias was elected by lots (Acts 1:18-26) to take the place left by Judas. Details of St. Matthias' life are scant, but it is believe he preached the Gospel in Judea and then Aethiopia. In leap years St. Matthias is celebrated on the 25th February.
Yesterday the Vigil of St. Matthias was commemorated in the Office of St. Peter Damian with its ninth lesson being read at Mattins and a commemoration at Lauds. At Mass yesterday a commemoration of the Vigil was sung and its Gospel read as the last Gospel. Celebration of the feast began with first Vespers yesterday afternoon. The antiphons Hoc est praeceptum meum etc were sung with the psalms for Vespers (Pss. 109, 110, 111, 112 & 116) from the Common of Apostles. The Common provided the chapter, hymn but the collect was proper to the feast. A commemoration was sung of the preceding Office of St. Peter Damian. At Compline the Dominical psalms were sung.
At Mattins the invitatory is Regem Apostolorum Dominum, venite adoremus. The antiphons In omnem terram etc are sung with the psalms from the Common of Apostles. In first nocturn the lessons are taken from the Acts of the Apostles. In the second nocturn the lessons are from an exposition on the eighty-sixth psalm by St. Augustine. In the third nocturn the homily is taken from a sermon of St. Augustine on St. Matthew's Gospel. At Lauds the antiphons Hoc est praeceptum meum etc are sung with the Sunday psalms.
At the Hours the antiphons from Lauds are used. At Prime the festal psalms are sung (Pss. 53, 118i, 118ii). The lectio brevis is Ibant Apostoli.
Mass is sung after Terce. The introit is Mihi autem nimis. The Gloria is sung, the Tract Desiderium animae is sung. The Creed is sung and the preface is of the Apostles.
Vespers are of the feast. At Compline the Dominical psalms are sung.
In the 'liturgical books of 1962' the Vigil has been abolished. The feast loses first Vespers and is not commemorated at Vespers of St. Peter Damian, ferial Compline was sung yesterday. At Prime the ferial antiphons and psalmody are used, the lectio brevis is of the season. At the other Little Hours the ferial antiphons and psalms are also sung. In the 'Ordinary Form' of the 1962 rite the feast is celebrated on May 14th.