"it suffices Us to be able to state that a commemoration of the supreme pontiff and prayers offered for him during the sacrifice of the Mass is considered, and really is, an affirmative indication which recognizes him as the head of the Church, the vicar of Christ, and the successor of blessed Peter, and is the profession of a mind and will which firmly espouses Catholic unity. This was rightly noticed by Christianus Lupus in his work on the Councils: “This commemoration is the chief and most glorious form of communion” (tome 4, p. 422, Brussels edition). This view is not merely approved by the authority of Ivo of Flaviniaca who writes: “Whosoever does not pronounce the name of the Apostolic one in the canon for whatever reason should realize that he is separated from the communion of the whole world” (Chronicle, p. 228); or by the authority of the famous Alcuin: “It is generally agreed that those who do not for any reason recall the memory of the Apostolic pontiff in the course of the sacred mysteries according to custom are, as the blessed Pelagius teaches, separated from the communion of the entire world” (de Divinis Officiis, bk. 1, chap. 12) ... The clear result of all this is that the Latin and Greek churches agree in recognizing and affirming that the commemoration implies a profession of due subjection to the Roman pontiff as head of the Church, and of a willingness to remain in the unity of the Church. On the other hand the omission of this commemoration signifies the intention of steadfastly espousing schism."
(Ex Quo, Pope Benedict XIV, from Papal Encyclicals: http://www.papalencyclicals.net/ben14/b14exquo.htm)