Bifolio from a Choir Book

Illuminated choir books contained numerous music and text selections which were appropriate both for the type of mass being celebrated and for the time of day. These volumes were impressively large so that the entire choir could read and sing from one book during the church service. The elaborately painted initials served as bookmarks.

A bifolio is a single sheet folded in half to make two leaves usually printed on both sides, as seen here.