COMMUNIO. – It is the antiphon that, in a Solemn Mass, is sung by the choir after the celebrant’s Communion; in all Masses it is simply read by the celebrant himself. Formerly it was sung during the distribution of Communion to the faithful, interspersed with verses of a psalm. Gradually the psalm was shortened until it disappeared entirely, so that only the antiphon remained, in which some thought of the day or feast being celebrated is summarized; a vestige of the ancient usage remains only in the Requiem Mass. In the Ambrosian rite it is called transitorium.
BIBL.: I. Schuster, *Liber Sacramentorum*, I, 3rd ed., Turin 1932, p. 100; III, ibid. 1933, p. 70; G. Destefani, *La Messa nella liturgia romana*, ibid. 1935, pp. 307, 751 ff.; Filippo Oppenheim