The Canon used in the Traditional Mass is the same as used by Pope Damascus in the years 366-384. Only two phrases were added, one by Pope Leo {440-461} and by Pope Gregory {540-604}.
The reading of scripture in one year cycles was established by St Damasus in the fourth century.
In the fifth century Pope Celestine I introduced the Introit and the Gradual.
In the sixth century Pope Gregory added the Kyrie Eleison
In the seventh Pope Sergius introduced the Agnes Dei…
Over the centuries various additions were made to the ceremonies surrounding the Canon. But the canon itself remained sacred and untouched.
When the Mass was being attacked by the reformers it was necessary to codify it so as to protect it from possible corruption.
The Traditional Mass therefore could never be forbidden or altered, as was declared by Pius V in Quo Primum.
Stmaria I would like to dispute your conclusion.
The source of this information is the Liber Pontificalis. I point out that in certain places the Liber is not always accurate and has to be taken with a pinch of salt. You will find it in scholars like Momsen and Duchesne that the accounts are only reliable from the contemporary age of the compiler (i.e. the 6th – 7th century)- from the 4th century they are to be taken into careful consideration- but earlier than that is probably pious ascription
The 26 words are presumably
sanctum sacrificium, immaculatam hostiam.-St. Leo I
diesque nostros in tua pace disponas, atque ab aeterna damnatione nos eripi, et in electorum tuorum jubeas grege numerari. Per Christum Dominum nostrum.- St. Gregory the Great
(Actually this works out to 27- and actually also I don’t think it is said that St. Gregory did added Per Christum)
Alternatively they could have (correctly) being referring to the 7 female saints of St. Gregory in the Nobis quoque but that doesn’t give an accurate number either.
Furthermore we can omit large other chnuks of the Canon like the Communicantes and the Nobis quoque as being Apostolic since they mention saints venerated later. Omit also the Memories igitur because that is a regular feature in all Masses only later, under Gallician influence.
Again certain features do give a disjointed look- like the Te igitur. What does igitur refer to? Some try and explain it away by saying that it is a continuation of the preface before the interpolation of the Sanctus but still that explanation does make it a tad clunky.
And there is actually no evidence to support that the Canon is completely apostolic. To begin with, the selfsame Liber implies a reworking of the Canon in its entries for Pope Gelasius and Gegory [and further in that vein the Stowe Missal also calls it the Canon of (Lord) Pope Gelasius. Not that it proves anything. But one would expect if it was apostolic that it would be given a name to rival other liturgies- like St. Peter or Holy Apostles].
St. Gregory can be seen as saying that it was written by a “scholasticus” [and even if one takes most other probable interpretations of his words, that still leaves the “scholasticus” with quite a big role]
This is not to say that the Canon is not ancient. I think it was Bouyer (excuse the lack of the quote, I’m on vacation and don’t have the stuff with me) who pointed out various features such as the different order of the apostles, the use of martyrs only (as presumed from the Gregorian versions) , the angelic epiclesis etc. that “savour of antiquity”. But not necessarily apostolic.
Evidence wise- the earliest expanded mention occurs in De Sacramentis by the pseudo-Ambrose. Whether it is Milanese recension or actual Roman, it only approximates very closely the part of the Canon from Quam oblationem to Supplices- it is not word for word. .
Also one final thing. It is not true that the Canon remained unchanged throughout the Middle Ages. In fact there were a lot of liberalities taken with some parts of the text sometimes, also rearrangement of texts, adding provate expansions of the prayers- as in the Stowe Missal- and additions to the saints and Hanc igitur.
As to the reading of Scripture. I’ll try and answer that a bit later in more detail but in short the Scriptre lection attribution comes from a tradition represented in documents known as the “Liber Comicus (or Comius)” which begins " Epistola sancti Hieronymi missa ad Constantium…" however other documents in the collection, and the preference to a certain Latin version of the Bible show that this is not entirely accurate. and so most scholars ascribe it not to St. Jerome but to Victor of Capua (and again it is not *entirely *exact as the lectionery of the missal and certain part lie the feriae are missing )
