consist of an incipit, a recitation formula, and a cadence, lacking the mediant flex found in Gregorian psalm tones. Other Vespers chants include the Psallendae and the Antiphonae in choro. Psallendae comprise the largest category of Ambrosian Office chants. Two Psallendae, similar to the Marian antiphons of Gregorian chant, are performed on the more solemn Vespers, to cover processions. They conclude with one of several recitation tones that segue into the Gloria Patri. Antiphonae in choro are similar in style, but have no psalm or verse. Responsoria occur in both Matins and Vespers. Their names often identify who is to sing them: the boys' choir, the deacon, the subdeacons, and so on. A Responsorium usually consists of a refrain called a respond, a verse, and a repetition of an expanded part of the respond. These expansions contain some of the longest melismas of the Ambrosian chant repertoire, which often contain complex repeat structures. Vespers begin with a chant called the Lucernarium and end with the Completorium. The word Lucernarium hearkens back to the original function of Vespers as a time of lighting lamps, and the texts of Lucernaria usually contain some reference to light, such as Quoniam tu illuminas, Paravi lucernam, and Dominus illuminatio. Stylistically, Lucernaria and Completaria vary. Some are proper, specific to certain feasts, while others are ordinary and can be used throughout the year. They range from highly elaborate chants to simple reciting tones. There are relatively few Lucernaria and Completaria; four Completaria are used for all but three days of the year. Chants of the Mass The Mass is the Christian celebration of the Eucharist. Plainchant occurs prominently in the Mass for several reasons: to communally affirm the faith, to expand on the scriptural lessons, and to accompany certain actions. The chants of the Mass divide into the ordinary, whose texts are invariable, and the proper, whose texts change depending on the feast. There are several differences between the Ambrosian rite and the Roman rite, which are reflected in the Ambrosian and Gregorian chant traditions. Ordinary chants of the Mass The ordinary chants consist of the Laus Missa or Gloria, the Symbolum, and the Sanctus. The Symbolum corresponds to the Credo in the Roman rite. Unlike Gregorian chant, there is no Agnus Dei nor Ite missa est, and the Kyrie does not exist as a separate category of chant. Only a small number of each of