Book of Hours were prayer books designed for the laity, but modeled on the Divine Office, a cycle of daily devotions, prayers and readings, performed by members of religious orders and the clergy. Its central text is the Hours of the Virgin. There are eight hours (times for prayer ): Matins, Lauds. Prime, Terce, Sext, None, Vespers and Compline. During the Middle Ages, the leaves making up a Book of Hours were written by hand on expensive parchment and beautifully illuminated with jewel-like pigments and gold leaf. These illuminated manuscripts combined the collaborative efforts of an array of highly skilled craftspeople; requiring the joint labors of the parchmenter, professional scribes to write the text in Gothic script, artists to illuminate the pages with decorations, and masterful binders to complete the process.

A very pretty leaf from a Parisian Book of Hours, written on a fine sheet of buttery, white vellum in black ink. The leaf is decorated with one large and three small initials as well as one line filler illuminated in red, blue, white and burnished gold leaf. Both sides feature decorative panels painted with gold leaves on hairline stems with colorful flowers and fruits. The text is from a hymn composed by Venantius Fortunatus (530-609), Bishop of Poitiers, and was an important part of devotions to the Blessed Virgin Mary beginning in the early Middle Ages. Beginning on verso at the large initial "Q" the text reads (with a few abbreviations):

Quem terra, pontus, aethera colunt, adorant, praedicant, trinam regentem machinam claustrum Mariae baiulat.
Cui Luna, Sol, et omnia deserviunt per tempora, perfusa caeli gratia, gestant Puellae viscera.
Beata Mater, munere, cuius supernus Artifex, mundum pugillo continens, ventris sub arca clausus est.

This translates into English as:
The God whom earth, and sea, and sky adore, and laud, and magnify, who o'er their threefold fabric reigns, the Virgin's spotless womb contains.
The God whose will by moon, and sun, and all things in due course is done, is borne upon a Maiden's breast, by fullest heavenly grace possessed.
How blest that Mother, in whose shrine the great Artificer Divine, whose hand contains the earth and sky, vouchsafed, as in His ark, to lie.

References:

Condition: A

Marginal soiling.