Round its top run balustrades formed of Gothic letters, which read as part of the Magnificat.
The text is from the Magnificat antiphon of second Vespers at the feast of Corpus Christi.
Fortunately, however, the Gregorian canto fermo associated with it is of exceptional beauty and symmetry; and the great 16th century masters either, like Palestrina, left it to be sung as plain-chant, or obviated all occasion for dramatic expression by setting it in versicles (like their settings of the Magnificat and other canticles) for two groups of voices alternatively, or for the choir in alternation with the plain chant of the priests.
In it the Pater Noster, Ave Maria, Deus in Adjutorium, &c., are followed by five psalms and five antiphons, after which come the "little chapter," the hymn and the verse, which vary according to the season, the Magnificat and its antiphon, and the appropriate collect.