What if the psalm is long?
124. When longer psalms occur, sections are marked in the psalter that divide the parts in such a way as to keep the threefold structure of the hour; but great care has been taken not to distort the meaning of the psalm.
It is useful to observe this division, especially in a choral celebration in Latin; the Glory to the Father is added at the end of each section.
It is permissible, however, either to keep this traditional way or to pause between the different sections of the same psalm or to recite the whole psalm and its antiphon as a single unit without a break.
When may the antiphon be repeated after each strophe?
125. In addition, when the literary genre of a psalm suggests it, the divisions into strophes are marked in order that, especially when the psalm is sung in the vernacular, the antiphons may be repeated after each strophe; in this case the Glory to the Father need be said only at the end of the psalm.