I am researching the Tridentine Mass and found a book called "The Meaning of the Mass" by Rev. Paul Bussard (copyright 1942). It is an excellent book, but I found something in it which is confusing because I cannot seem to find a source or confirmation for it anywhere else.

Father Bussard says that Psalm 42 (Judica Me), which is recited at the beginning of the Mass, has a special significance because it was once used in the processions of the Catechumens as they were going to be baptized.

Here is the passage in question, judiciously snipped:

The recitation of Psalm 42 in preparation for Mass has a remarkable history, the knowledge of which should make it mean more to us than it does...It was formerly a song of Baptism. We recall that Catechumens were baptized on Easter Saturday. Immediately after Baptism, they marched in procession to take part in the Mass and to receive Holy Communion for the first time...As they walked thus along,...they sang, "I will go to the altar of God, to God who is the joy of my youth."

This is a beautiful significance indeed, but I cannot find any other source that makes this claim. In fact, the only reference I've found to the use of Psalm 42 in Baptismal Processions appears to in fact refer to Psalm 41 (Sicut Cervus), and I'm wondering whether confusion arising from the numbering of Psalms in the Vulgate vs. Modern Bibles is at the base of this claim? Psalm 41 is renumbered in Bibles proceeding from the KJV, etc. as Psalm 42.

Does anyone know anything about this and can point me in the right direction? I've tried looking at Augustine's Exposition of the Psalms (which, though available online at New Advent, is confusingly listed under the modern numbering, not the Vulgate numbering...) and I've heard that this matter is mentioned in the Gelasian Sacramentary, but I can't find it there...

I would love to hear more if anyone knows???