Music Pages
"In late mediaeval times, when it had become common in the West for priests to say Mass without the assistance of a choir and other ministers, these books began to be combined into a "Mass book", for the priest's use alone. This led to the appearance of the missale plenum ("full or complete missal"), which contained all the texts of the Mass, but without the music of the choir parts."
"Missale plenum." Encyclopædia Britannica. Encyclopædia Britannica Online Academic Edition. Encyclopædia Britannica Inc., 2012. Web. 05 May. 2012