Catholic Encyclopedia (1913)/Roman Processional
Strictly speaking it might be said that the Processional has no recognized place in the Roman series of liturgical books. As the full title of the work so designated shows, the book consists of a, single section of the Roman Ritual (titulus ix) with sundry supplementary materials taken from the Missal and the Pontifical. What we read on the title-page of the authentic edition runs as follows: "Processionale Romanum sive Ordo Sacrarum Processionum ex Rituali Romano depromptus additis quae similia in Missali et Pontificali habentur". Seeing, however, that the Ritual does not always print in full the text of the hymns, litany, and other prayers which it indicates, it is convenient to have these set out at length with the music belonging to them. Processionals appropriated to the special uses of various local churches, e.g. "Processionale as usum Sarum", are of fairly common occurrence among the later medieval manuscripts. At the close of the fifteenth century and in the beginning of the sixteenth we have a good many printed processionals belonging to different churches of France, England, and Germany.
ZACCARIA, Bibliotheca ritualis, I (Rome, 1776), 159.