The text and melody below were already in existence before the time of Thomas Aquinas in Monday of the Octave of Pentecost. See (among many) Codex Bodmer 74, p.106v,

See the following 12th century Ms Clm 2541, from Bayerische StaatsBibliothek, p. 199,
Contra, O per omnia laudabilem virum, de sancto Nicholao.
After looking at innumerable manuscripts, I did not find this Introitus/Officium for St. Nicholas. They refer rather to "Statuit" or "Sacerdotes Dei" from the Commons. But the text is that of the 5th antiphon for Lauds of his feast:

Here is an attempt to follow Thomas' instruction, adding the final two (8th tone) Alleluias from Pentecost:

He fed them with the best wheat,
and replenished them with honey from the rock.
[Note: This trope was not composed by Thomas Aquinas, but was in circulation in his time. It fits the following "Roman" Kyrie fons bonitatis, which is not among Dominican Mass chants.]
Deus qui nobis sub sacramento mirabili passionis tuae memoriam reliquisti, tribue, quaesumus, ita nos corporis et sanguinis tui sacra mysteria venerari, ut redemptionis tuae fructum in nobis iugiter sentiamus. Qui vivis et regnas cum Deo patre in unitate spiritus sancti Deus per omnia saecula saeculorum. Amen.

God, in this wonderful sacrament you left us a memorial of your Passion. Enable us, we ask, so to venerate the sacred mysteries of your Body and Blood, that we may always fell the fruit of your redemption in us. You live and reign with God the Father in the unity of the Holy Spirit, forever and ever. Amen.
Lectio epistolae beati Pauli apostoli ad Corinthios (11:23-29)
Fratres, ego enim accepi a domino quod et tradidi vobis; quoniam dominus Iesus in qua nocte tradebatur, accepit panem, et gratias agens fregit et dixit: accipite et manducate: hoc est corpus meum, quod pro vobis tradetur; hoc facite in meam commemorationem. Similiter et calicem, postquam cenavit, dicens: hic calix novum testamentum est in meo sanguine; hoc facite, quotiescumque sumitis, in meam commemorationem. Quotiescumque enim manducabitis panem hunc et calicem bibetis, mortem domini annuntiabitis donec veniat. Itaque quicumque manducaverit panem vel biberit calicem domini indigne, reus erit corporis et sanguinis domini. Probet autem seipsum homo; et sic de pane illo edat, et de calice bibat. Qui enim manducat et bibit indigne, iudicium sibi manducat et bibit, non diiudicans corpus domini.
For I received from the Lord what I also handed on to you, that the Lord Jesus, on the night he was handed over, took bread, and, after he had given thanks, broke it and said, "This is my body that is for you. Do this in remembrance of me." In the same way also the cup, after supper, saying, "This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me." For as often as you eat this bread and drink the cup, you proclaim the death of the Lord until he comes. Therefore whoever eats the bread or drinks the cup of the Lord unworthily will have to answer for the body and blood of the Lord. A person should examine himself, and so eat the bread and drink the cup. For anyone who eats and drinks without discerning the body, eats and drinks judgment on himself.
Gradualis (Borrowed from Thursday, third week of Lent)

℟. The eyes of all hope in you, Lord, and you give them their food in due time.
℣. You open your hand, and fill every living thing with blessing.

My flesh is really food, and my blood is really drink. He who eats my flesh and drinks my blood dwells in me, and I in him.
Contra, Nativitas gloriosa, de sancta Maria.

The contra text —Numbers correspond in melody, with minor variants, to those of Lauda Sion.
2. Laudes crucis attolamus/ nos qui crucis exultamus/ speciali gloria.
Let us raise praise of the cross, we who exult with the cross's special glory.
3. Dulce melos pulset celos/ dulce lignum dulci dignum/ credimus melodia.
Let sweet melody knock on heaven; the sweet wood we believe is worthy of song.
4. Voci vita non discordet/ dum vox vitam non remordet/ dulcis est simphonia.
Let life not discord with voice. When voice does not blame life, the harmony is sweet.
5. Servi crucis crucem laudent/ qui per crucem sibi gaudent/ vite dari munera.
Let the servants of the cross praise the cross, who rejoice that through the cross they are given the gifts of life.
6. Dicant omnes et dicant singuli/ ave salus totius seculi/ arbor salutifera.
Let one and all say: Ave, saving tree, salvation of the whole world.
7. O quam felix quam preclara/ fuit hec salutis ara/ rubens agni sanguine.
How happy and beautiful was this altar of salvation, red with the Lamb's blood—
8. Agni sine macula/ qui mundavit secula/ ab antiquo crimine.
That Lamb without blemish, who cleansed the world from the ancient crime.
9. Hec est scala peccatorum/ per quam Christus rex celorum/ ad se traxit omnia.
This is the ladder of sinners, through which Christ, the king of heaven, drew all things to himself.
10. Forma cuius hec ostendit/ que terrarum comprehendit/ quatuor confinia.
Its form shows that it embraces the four reaches of the earth.
11. Non sunt nova sacramenta/ nec recenter est inventa/ crucis hec religio.
Here are not unprecedented sacraments, nor is this religion of the cross newly invented.
12. Ista dulces aquas fecit/ per hanc silex aquas iecit/ Moysi officio.
But it made the water sweet; by it the flit spewed out water, at the hand of Moses.
13. Nulla salus est in domo/ nisi crucem munit homo/ super liminaria.
There was no salvation in a home, unless the owner armed it with a cross on its lintel.
14. Neque sentit gladium/ nec amisit filium/ quisque egit talia.
Whoever did that felt no sword, nor lost any child.
15. Ligna legens in Sarepta/ spem salutis est adepta/ pauper muliercula.
The poor widow, gathering wood in Sarepta, won hope of salvation.
16. Sine lignis fidei/ nec lecitus olei/ valet ne farinula.
Without the wood of faith, her wheat and jar of oil would be worthless.
17. In scripturis sub figuris/ ista latent sed iam patent/ crucis beneficia.
The benefits of the cross hide under figures in the Old Testament, but now they are apparent.
18. Reges credunt hostes cedunt/ sola cruce Christo duce/ unus fugat milia.
Kings believe, enemies give way. By the cross alone, with Christ the commander, one soldier drives away a thousand.
19. Ista suos fortiores/ semper facit et victores/ morbos sanat et languores/ reprimit demonia.
The cross always makes its own stronger and victorious, it heals sickness and weakness, and represses demons.
20. Dat captivis libertatem/ vite confert novitatem/ ad antiquam dignitatem/ crux redemit omnia.
The cross gives liberty to captives, renews life to its former dignity, and redeems everything.
21. O crux lignum triumphale/ mundi vera salus vale/ inter ligna nullum tale/ fronde flore germine.
O cross, triumphal wood, hail the world's true salvation. Among all trees, there is no comparison, with its leaves, flowers and fruit.
22. Medicina christiana/ salva sanos egros sana/ quod non valet vis humana/ fit in tuo nomine.
Medicine of Christians, save the healthy, heal the sick. What human strength cannot do, happens in your name.
23. Assistentes crucis laudi/ consecrator crucis audi/ atque servos tue crucis/ post hanc vitam vere lucis/ transfer ad pallacia.
Consecrator of the cross, hear us present praising the cross, and after this life transfer the servants of your cross to [their heavenly] palaces.
24. Quos tormentis vis servire [= seviri?]/ fac tormenta non sentire/ et cum dies venit ire/ nobis confer et largire/ sempiterna gaudia.
Those you wish to be ravished by torment [I take "servire" ("to serve torment") as a copyist's error for seviri (saeviri)], let them not feel the torment. And when the day come for us to go, grant us eternal joy.

I provisionally offer the translation of "Msgr. Henry" (slightly modified):
Praise, O Sion, praise your Savior,
Shepherd, Prince, with glad behavior,
Praise in hymn and canticle:

Sing His glory without measure,
For the merit of your Treasure
Never shall your praises fill.

Wondrous theme of mortal singing,
Living Bread and Bread life-bringing.
Sing we on this joyful day:

At the Lord's own table given
To the twelve as Bread from Heaven,
Doubting not we firmly say.

Sing His praise with voice sonorous;
Every heart shall hear the chorus
Swell in melody sublime:

For this day the Shepherd gave us
Flesh and blood to feed and save us,
Lasting to the end of time.

At the new King's sacred table,
The new Law's new Pasch is able
To succeed the ancient Rite:

Old to new its place hath given,
Truth has far the shadows driven,
Darkness flees before the Light.

And as He hath done and planned it-
"Do this"-hear His love command it,
"For a memory of me."

Learned, Lord in Your own science,
Bread and wine, in sweet compliance,
As a Host we offer You.

Thus in faith the Christian heareth:
That Christ's Flesh as bread appeareth,
And as wine His Precious Blood:

Though we feel it not nor see it,
Living Faith that doth decree it
All defects of sense makes good.

Lo! beneath the species dual
(Signs not things), is hid a jewel
Far beyond creation's reach!

Though His Flesh as food abideth,
And His Blood as drink-He hideth
Undivided under each.

Whoso eateth It can never
Break the Body, rend or sever;
Christ entire our hearts doth fill:

Thousands eat the Bread of Heaven,
Yet as much to one is given:
Christ, though eaten, bideth still.

God and bad, they come to greet Him:
Unto life the former eat Him,
And the latter unto death;

These find death and those find heaven;
See, from the same life-seed given,
How the harvest differeth!

When at last the Bread is broken,
Doubt not what the Lord hath spoken:
In each part the same love token,
The same Christ, our hearts adore:

For no power the Thing divideth-
'Tis the symbols He provideth,
While the Saviour still abideth
Undimished as before.

Hail, angelic Bread of Heaven,
Now the pilgrim's hoping-leaven,
Yea, the Bread to children given
That to dogs must not be thrown:

In the figures contemplated,
'Twas with Isaac immolated,
By the Lamb 'twas antedated,
In the Manna it was known.

O Good Shepherd, still confessing
Love, in spite of our transgressing,-
Here Your blessed Food possessing,
Make us share Your every blessing
In the land of life and love:

Thou, whose power hath all completed
And Your Flesh as Food hath meted,
Make us, at Your table seated,
By Your Saints, as friends be greeted,
In Your paradise above.

Contra, Laudes crucis attolamus, de sancta Cruce (below, at border).
Exaltatio S. Crucis f. 327v-330v, Universittsbibliotek, Graz, 15th c. & Ms. 0017
Inventio S. Crucis, ibid., f. 290v-291v.

Secundum Ioannem (6:56-58)
In illo tempore dixit Iesus discipulis suis et turbis Iudaeorum: Caro mea vere est cibus, et sanguis meus vere est potus. Qui manducat meam carnem et bibit meum sanguinem, in me manet et ego in illo. Sicut misit me vivens pater, et ego vivo propter patrem; et qui manducat me, et ipse vivet propter me. Hic est panis qui de caelo descendit. Non sicut manducaverunt patres vestri manna, et mortui sunt: qui manducat hunc panem, vivet in aeternum.
Whoever eats my flesh and drinks my blood remains in me and I in him. Just as the living Father sent me and I have life because of the Father, so also the one who feeds on me will have life because of me. This is the bread that came down from heaven. Unlike your ancestors who ate and still died, whoever eats this bread will live forever."


The priests of the Lord will offer incense and bread to God, and therefore they shall be holy for their God, and shall not pollute his name. Halleluia. (Cf. Lev 21:6)
Ecclesiae tuae, quaesumus, domine, unitatis et pacis propitius dona concede, quae sub oblatis muneribus mystice designantur.

To your Church, we ask O Lord, kindly give the gifts of unity and peace, which the gifts we offer mystically signify.
Praefatium (de Nativitate domini)
Sanctus 1
Agnus Dei

I will sing to the Lord who bestowed good things on me, and I will sing to the name of the Lord Most High.
Fac nos, quaesumus, domine, divinitatis tuae sempiterna fruitione repleri, quam pretiosi corporis et sanguinis tui temporalis perceptio praefigurat. Qui vivis et regnas cum Deo patre in unitate spiritus sancti Deus per omnia saecula saeculorum. Amen.

We ask, O Lord, always to be filled with the enjoyment of your divinity, which this temporal reception of your body and blood prefigures.