A Dictionary of Music and Musicians (1900)
“ The first, and one of the most important, of these, is the Introit; which partakes, in about equal degrees, of the characters of the Antiphon and the Psalm Tone. The words of the Introit are divided into two portions, of which the first is a pure Antiphon, and the second, a single Verse of a Psalm, followed by the 'Gloria Patri,' after which the Antiphon is again repeated in full. Except that it is perhaps a little more elaborate, the Melody of the first division differs but little, in style, from that proper to the Antiphons sung at Lauds and Vespers ”
