The service for a given day’s Office or Mass is usually pieced together from both common (meaning “shared”) and proper (in the sense of “particular to”) segments that occur in a liturgical book at different points. The most immediately visual example of this is the frequent placement of the text for the Canon of the Mass (an “ordinary” text in that it is used for all Masses) directly before Easter Sunday. The result is that the Canon occurs at the middle of the book, and many manuscript missals will almost fall open by themselves to that section from the heavy use it has received over the years. Another example of disjuncture between practice in the service and placement in the book is the Kyrie: although it is sung towards the beginning of the Mass, the Kyrie was usually copied with its various musical settings at the end of the graduals.
The dispersed arrangement of texts certainly caused problems to young monks and priests during the Middle Ages. In 1274 a visiting French cleric endorsed with enthusiasm a system he first saw in the liturgical books in the papal chapel in Avignon: the leaves were numbered, so that when one needed to go to another part of the book to complete a service, one could quickly find the right passage without suffering the embarrassment of ignorance in attempts to turn to the right page (“nec ruborem de imperitia nesciendi volvere patieris”). While foliation of the big antiphoners and graduals became common in Italy during the 15th century, pagination and the indexes that refer to it were an innovation of the 16th century’s printed book.