ChapterIII-V. Canticles From the Old and New Testaments
136. At morning prayer between the first and the second psalm a canticle from the Old Testament is inserted, in accordance with custom. In addition to the series handed down from the ancient Roman tradition and the other series introduced into the breviary by St. Pius X, several other canticles have been added to the psalter from different books of the Old Testament, in order that each weekday of the four-week cycle may have its own proper canticle and on Sunday the two sections of the Canticle of the Three Children may be alternated.
137. At evening prayer, after the two psalms, a canticle of the New Testament is inserted, from the letters of the apostles or the Book of Revelation. Seven canticles are given for each week of the four-week cycle, one for each day. On the Sundays of Lent, however, in place of the Alleluia Canticle from the Book of Revelation, the canticle is from the First Letter of Peter. In addition, on the solemnity of the Epiphany and the feast of the Transfiguration the canticle is from the First Letter to Timothy; this is indicated in those offices.
138. The gospel Canticles of Zechariah, of Mary, and of Simeon are to be treated with the same solemnity and dignity as are customary at the proclamation of the gospel itself.
139. Both psalmody and readings are arranged in keeping with the received rule of tradition that the Old Testament is read first, then the writings of the apostles, and finally the gospel.