In Eucharistic Prayer IV, the Confitemur tibi, Pater sancte (Father, we acknowledge) up to and including the words omnem sanctificationem compleret (bring us the fullness of grace) is spoken by the principal celebrant alone, with hands extended.
From the Quaesumus, igitur, Domine (Father, may this Holy Spirit) to the Respice, Domine (Lord, look upon the sacrifice) inclusive, all the concelebrants speak all the following together: The Quaesumus igitur, Domine (Father, may this Holy Spirit) with hands extended toward the offerings; The Ipse enim, cum hora venisset (He always loved those) and the Simili modo (When supper was ended) with hands joined; While speaking the words of the Lord, each extends his right hand toward the bread and toward the chalice, if this seems appropriate; as the host and the chalice are shown, however, they look toward them and afterwards bow profoundly; The Unde et nos (Father, we now celebrate) and the Respice, Domine (Lord, look upon this sacrifice) with hands outstretched.
The intercessions Nunc ergo, Domine, omnium recordare (Lord, remember those) and Nobis omnibus (Father, in your mercy) are appropriately assigned to one or other of the concelebrants, who speaks them aloud alone, with hands extended.
As to other Eucharistic Prayers approved by the Apostolic See, the norms established for each one are to be observed.
The concluding doxology of the Eucharistic Prayer is spoken solely by the principal priest celebrant and, if this is desired, together with the other concelebrants, but not by the faithful.