Mystici Corporis Christi §27

²⁷ For while fulfilling His office as preacher He chose Apostles, sending them as He had been sent by the Father - namely, as teachers, rulers, instruments of holiness in the assembly of the believers; He appointed their Chief and His Vicar on earth; He made known to them all things and whatsoever He had heard from His Father; He also determined that through Baptism those who should believe would be incorporated in the Body of the Church; and finally, when He came to the close of His life, He instituted at the Last Supper the wonderful Sacrifice and Sacrament of the Eucharist.