A highly interesting and not too straight-forward day in the Traditional rite. The double rank feast of SS Eustace and his Companions falls on the Ember Saturday of September. It is also the Vigil of St. Matthew the Apostle.
The Vigil is not commemorated in the Office (because of the Ember Day). The feast is of double rank and was 'from the chapter' of Vespers on Friday. At Mattins in the first nocturn the lessons are from the previous Tuesday (as these were not read because of having to resume the previous Sunday's readings, from the beginning of the Book of Tobias, due to the occurence of the Feast of the Exaltation of the Holy Cross on the XVIII Sunday after Pentecost). Ordinarily ferial lessons are not transferred but because of the Ember Days a rubric in the Breviary on Monday prescribes that if the lessons of Monday and Tuesday of the third week of September are not read then they are transferred to an Ember Day if recourse to the common would otherwise have to be made. So this year Monday's lessons were read on Friday and Tuesday's lesson are read today. In the third nocturn the ninth lesson is of the Ember Saturday. At Lauds there is a commemoration of the Ember Saturday.
In the festal Mass, sung after Terce, there is the Gloria, the second collect of the Ember Saturday (the first oration, Omnipotens sempiterne Deus, after the Kyrie from the Ember Saturday texts), the third collect is of the Vigil and the last Gospel of the Ember Saturday.