the funeral rites of the Anglican Book of Common Prayer. Other well-known sequences include the ninth-century Swan Sequence, Tommaso da Celano's Dies Irae, St. Thomas Aquinas' Pange lingua in praise of the Eucharist, the anonymous medieval hymn Ave maris stella ("Hail, star of the sea!"), and the Marian sequence Stabat Mater by Jacopone da Todi. During the Middle Ages, secular or semi-secular sequences, such as Peter of Blois' Olim sudor Herculis ("The labours of Hercules") were written; the Goliards, a group of Latin poets who wrote mostly satirical verse, used the form extensively. The Carmina Burana is a collection of these sequences. Many sequences abolished In the Missal of Pius V (1570) the number of sequences for the entire Roman Rite was reduced to four: Victimae paschali laudes (11th century) for Easter, Veni Sancte Spiritus for Pentecost (12th century), Lauda Sion Salvatorem (c.1264) for Corpus Christi, and Dies Irae (13th century) for All Souls and in Masses for the Dead. In 1727, the 13th century Stabat Mater for Our Lady of Sorrows was added to this list. In 1970 the Dies Irae was removed from the Requiem Mass of the revised, new Roman Missal and was transferred to the Liturgy of the Hours to be sung ad libitum in the 34th week of the Ordinary Time before the beginning of Advent, dividing into three parts: Office of Readings, Lauds and Vespers. Currently, the Dies Irae is sung in churches where the Tridentine Mass is celebrated. The Christmas sequence Laetabundus, not present in the Roman Missal, is found in the Dominican Missal. This sequence is permitted for the Third Mass of Christmas, the Epiphany, and Candlemas. The Third Edition of the Roman Missal, which was implemented in the United States in 2010, states that the Sequence is optional except on Easter Sunday and Pentecost Day, and it sung before the Alleluia. The sequence as a musical genre Sequences are distinguished by a structure dominated by couplets, in forms of AA'BB'CC'... and ABB'CC'DD'...Z. Although it is commonly understood that sequences fall into early, middle, and late periods, the history of developments in the genre is better thought of as unfolding in layers that overlap. In the early period, sequences such as Notker's often included single lines that were not part of a couplet. These single lines most often appeared at the beginning or end of the sequence, but could also appear in