38. Finally, it was custom in both the western and the eastern church for the priests to offer Mass together with the bishop. The evidence is collected by Christianus Lupus in the Appendix on the Council of Chalcedon in his ad Concilia Generalia, et Provincialia, vol. 1, p. 994, of the first edition, where he interprets the words of Bassianus: "He used to celebrate Masses with me and to communicate with me"; and by Georgius, Lyturgiae Pontificiae, vol. 2, p. lf, and vol. 3, p. lf. The rite of concelebration is now out of fashion in the western church, except at priestly ordinations performed by the bishop and at episcopal consecrations where two bishops assist the consecrating bishop. But this rite continues to thrive in the Oriental Church, and priests often concelebrate with the bishop or with the priest as chief celebrant. This practice is derived from the Apostolic Constitutions, bk. 8, and the eighth Apostolic Canon. And wherever this custom is practiced among Greeks and Orientals, it is approved and to be preserved as We command in Our constitution Demandatam, sect. 9.