The list of Saints in the Ambrosian Nobis quoque begins with “John and John”; these are evidently the Baptist and the Apostle, the latter of whom is named earlier in the Communicantes. It is not clear why the church of Milan felt the need to repeat the name of the Apostle, but he is not the only one named twice. After St. Stephen the First Martyr, who comes after John as in the Roman Rite, St. Andrew’s name is also repeated; St. Matthias, who took the place of the traitor Judas, is omitted. There are of course other early saints named John and Andrew, but none of them is particularly prominent, or has any obvious connection with Milan.
St. Barnabas’ name was added to the Canon by the revision of St. Charles Borromeo, in reference to a late and unreliable tradition that he was the first bishop of Milan; it does not appear in any earlier printed edition or manuscript of the Ambrosian Missal, despite its presence in the Roman Canon. Ss. Ignatius of Antioch and Alexander are omitted, and the list of male martyrs is completed by Ss. Peter and Marcellinus, who are named in the opposite order from the Roman Canon. Their church in Rome was one of the first basilicas built in the city, by the Emperor Constantine himself, and would also have been known to St. Ambrose.
St. Barnabas’ name was added to the Canon by the revision of St. Charles Borromeo, in reference to a late and unreliable tradition that he was the first bishop of Milan; it does not appear in any earlier printed edition or manuscript of the Ambrosian Missal, despite its presence in the Roman Canon. Ss. Ignatius of Antioch and Alexander are omitted, and the list of male martyrs is completed by Ss. Peter and Marcellinus, who are named in the opposite order from the Roman Canon. Their church in Rome was one of the first basilicas built in the city, by the Emperor Constantine himself, and would also have been known to St. Ambrose.
All of the female martyrs named in the Roman canon are included in the Ambrosian, but in a different order, with six other women added to their company. Ss. Agnes and Cecilia, two Romans, begin the list, followed by Ss. Felicity and Perpetua, who were martyred together at Carthage in 202 A.D. St. Anastasia, devotion to whom was formerly very important in Rome, follows; the Roman basilica dedicated to her is the station church for the Dawn Mass of Christmas, at which she is still commemorated in the traditional rite.
Ss. Agatha and Lucy, both Sicilians, are named next to each other in the Roman Canon; in the Ambrosian, St. Euphemia of Chalcedon, a martyr of the persecution of Diocletian, is placed between them. The church built over her grave was the site of the fourth ecumenical council, and in the Byzantine Rite, she is called a “Great Martyr.” In the Roman Rite, she is traditionally kept only as a commemoration on September 16th, the feast of Ss. Cornelius and Cyprian; Milan has kept her feast with greater prominence, preferring to move the two bishops to another day.
After Agatha, Euphemia and Lucy, St. Justina of Padua is named; traditionally venerated as a virgin martyr, nothing is really known of her for certain. She may have been killed in the persecution of Diocletian, but in the Middle Ages, she was said to be a disciple of St. Prosdocimus, who was sent by the Apostle Peter to evangelize the city. As mentioned earlier à propos of Ravenna, the whole of northern Italy was part of the ecclesiastical province of Milan in the patristic era; this might explain why a fairly obscure non-Milanese martyr was added to the Canon. The chapel of the university of Pavia, very close to Milan, was dedicated to St. Justina by St. Charles.
Ss. Agatha and Lucy, both Sicilians, are named next to each other in the Roman Canon; in the Ambrosian, St. Euphemia of Chalcedon, a martyr of the persecution of Diocletian, is placed between them. The church built over her grave was the site of the fourth ecumenical council, and in the Byzantine Rite, she is called a “Great Martyr.” In the Roman Rite, she is traditionally kept only as a commemoration on September 16th, the feast of Ss. Cornelius and Cyprian; Milan has kept her feast with greater prominence, preferring to move the two bishops to another day.
After Agatha, Euphemia and Lucy, St. Justina of Padua is named; traditionally venerated as a virgin martyr, nothing is really known of her for certain. She may have been killed in the persecution of Diocletian, but in the Middle Ages, she was said to be a disciple of St. Prosdocimus, who was sent by the Apostle Peter to evangelize the city. As mentioned earlier à propos of Ravenna, the whole of northern Italy was part of the ecclesiastical province of Milan in the patristic era; this might explain why a fairly obscure non-Milanese martyr was added to the Canon. The chapel of the university of Pavia, very close to Milan, was dedicated to St. Justina by St. Charles.
The Basilica of Saint Justina in Padua, resting place of the relics of St Luke the Evangelist. The congregation of Cassinese Benedictines began as a reform of the monastery attached to this church, and was long known as the Congregation of Santa Giustina. There follows the Roman widow Sabina, another saint of very uncertain history; her acts claim that she was converted by a Syrian serving girl named Serapia, and that both of them were martyred under Hadrian, a month apart from each other. In the Roman Rite, she is kept as a commemoration on August 29th, the feast of the Beheading of St. John the Baptist; oddly enough, she is not kept with a feast at all in the Ambrosian liturgy.
The Duomo of Milan as it stands today is the result of a project which began in 1386, to replace the two cathedrals which had hitherto served the see of St. Ambrose. The “winter church” as it is still called in Ambrosian liturgical books, was the smaller of the two, dedicated to the Virgin Mary, and used from the Third Sunday of October, the feast of its Dedication, until Holy Saturday; it stood where the modern cathedral stands, but was nowhere near as large. The larger “summer church”, which was demolished in 1543, stood on the opposite end of the modern Piazza del Duomo, and was dedicated to St. Thecla, for which reason her name is included in the Canon of the Mass. The apocryphal work in which her life is recorded, The Acts of Paul and Thecla, enjoyed great popularity in ancient times and into the Middle Ages, even though it was exposed as a forgery in the middle of the second century; she was greatly venerated by the many of the Church Fathers. In these Acts, Thecla is said to have been the first to heed St. Paul’s exhortation to virginity as a superior way of life; having refused marriage to a nobleman, she was put to various torments, but miraculously delivered from them all, and died at Iconium in Asia Minor at a great old age. The Byzantine Rite calls her “First-martyr among women and Equal-to-the-Apostles”; she is also named in the traditional form of the Prayers for the Dying, “As Thou (Lord) didst deliver Thy most blessed Virgin and Martyr Thecla from three most dreadful torments, so also mayest Thou deign to deliver the soul of Thy servant.”
The façade of the Duomo, completed in 1812. Note the plaque over the main door, with the simple inscription "Mariae Nascenti - to Mary being born." The feast of the Virgin's Nativity is the patronal feast of the church. Thecla is followed by St. Pelagia, a Christian virgin of Antioch martyred in the persecution of Diocletian. When soldiers came to kill her, knowing that she would be likely be raped first, she threw herself off the roof of her house; St. John Chrysostom, who was born in Antioch less than fifty years later, says that she was permitted to do so by a peculiar inspiration of the Holy Ghost. St. Ambrose devotes a passage to her in his book on Virginity (III.32-37), and mentions her in one of his letter (ep. VII ad Simplicianum), for which reason her feast is kept by the church of Milan on October 8th.
Finally, the name of St. Catherine of Alexandria, one of the most popular saints in the High Middle Ages, was added to early printed editions of the Ambrosian Missal, although it is not found in any of the manuscripts, and carried over into the revision of St. Charles Borromeo. Prior to this addition, there were twelve women martyrs in the Ambrosian Canon, perhaps a deliberate imitation of the company of the twelve Apostles.
The relevant page of the Ambrosian Missal, from the 1712 edition published by the authority of Giuseppe Card. Archinto, archbishop of Milan from 1699-1712. 
