 One suggestion is that the symbolism of the "Caput" ("head" in Latin) has not been taken into account, and while the Sarum Rite chant melisma may have been used as the source, the mass was used for an entirely different purpose, one perhaps based on this symbolism.Suggestions for this center around the symbolic meaning of "head".Following is the Latin from the end of the Sarum antiphon, "Venit ad Petrum", with its English translation (KJV)