The priest keeps his hands joined: when, vested, he walks in procession for the celebration of a liturgy; when he is kneeling at prayer; when he moves from altar to chair or from chair to altar; when the liturgical books prescribe joined hands.
Similarly, ministers keep their hands joined when walking from place to place or when standing, unless they are holding something.
“Hands joined” means: “Holding the palms sideward and together before the breast, with the right thumb crossed over the left.”
--Cf. *Ceremonial of Bishops*, no. 107 and footnote no. 80 (citing *Caeremoniale Episcoporum*, ed. 1886, I, XIX, 1)