usage, the introit corresponds to the Entrance Antiphon and is sung or recited audibly throughout by the faithful. Text and liturgical use The antiphons of most Introits are taken from Psalms, though many come from other parts of Scripture. In some rare cases the antiphon is not from Scripture: "Salve, sancta parens", from the Christian poet Sedulius, who was imitating a line from book V of Virgil's Aeneid, is the antiphon used in the Tridentine form of the Roman Rite for common Masses of the Blessed Virgin Mary; the 1970 revision kept a Mass formula of the Blessed Virgin with that antiphon, but provided several alternatives. The words of the antiphons are related to the theme of the feastday or celebration and most frequently have something in common with the liturgical readings of the Mass. In the Tridentine Mass the Introit is no longer the first text used in the Mass. In Low Mass, the priest reads it only after the Prayers at the Foot of the Altar. Until 1908, even in sung Mass the choir began the Introit only after the priest had begun those prayers, but Pope Pius X restored the old arrangement whereby the Introit accompanied the entrance procession of the priest with the ministers. The Tridentine Mass has the priest read the Introit in the Missal even when it is also sung by the choir. It also has him make the sign of the cross, when reading it, a relic of the time when Mass began with it. Since the 1970 revision of the Roman Missal, the Entrance chant begins as the priest enters. Its purpose is to open the celebration, foster the unity of those who have been gathered, turn their thoughts to the mystery of the celebration, and accompany the procession. If there is no singing at the Entrance, the antiphon in the Missal is recited either by the faithful, or by some of them, or by a lector; otherwise, it is recited by the priest himself, who may even adapt it as an introductory explanation. If another rite immediately precedes Mass, such as the Palm Sunday procession or the various ceremonies that precede Mass at the Easter Vigil, Mass begins with the collect; there is no Entrance at that point and so no Entrance chant. Musical setting In the musical idiom of Gregorian chant, Introits normally take the form antiphon-verse-antiphon-doxology-antiphon. In the Tridentine