2. Before we reply to the question, it will be useful to make two remarks. The first has reference to the difference between the functions of the deacon and those of the assistant priest. If the celebrant be assisted by a deacon and sub-deacon, the assistant need not do more than place the Blessed Sacrament on the throne, and lower it thence at the proper time. He may also extract the Blessed Sacrament from the tabernacle before the exposition, and replace it therein after the Benediction. The office of assistant appears to have been instituted as a measure of precaution against the danger which might result from the near approach of the deacon's vestments to the lights, in case he took down the ostensorium, or to guard against other inconveniences. But there is no reason why the assistant should present the ostensorium to the celebrant when the deacon and sub-deacon are present.
We should remark, in the next place, that, according to the text of the Ceremoniale Episcoporum, and of the Instructio Clementina, the priest, after receiving the humeral veil, mounts the steps without the ministers, and himself takes the ostensorium. Authors prescribe that the deacon and sub-deacon should kneel on the highest step, and support the celebrant's cope during the benediction. In their absence, this is done by the master of ceremonies, or two clerks. When the benediction has been given, the priest having completed the circle, places the Blessed Sacrament in the corporal, genuflects, and descends with the sub-deacon, whilst the deacon restores the Blessed Sacrament to the tabernacle, unless this be done by the assistant priest, in which case the deacon descends with the celebrant and the sub-deacon. According to Baldeschi, the veil is removed from the celebrant when he genuflects in the predella, after having given the benediction.
The rubric of the Ceremoniale Episcoporum (l. ii. c. xxiii., n. 27) makes no mention of the assistant priest, supposes that the bishop himself takes the ostensorium from the altar, and expressly declares that he himself replaces it on the corporal.
"Accedat ad altare et accepto tabernaculo seu ostensorio cum sanctissimo Sacramento, illud ambabus manibus velatis elevatum tenens, vertens se ad populum, cum illo signum crucis super populum ter faciet nihil dicens. Quo facto iterum deponet sanctissimum Sacramentum super altare".
We read in the Instructio Clementina (§ xxxi.): "The celebrant, on his knees, will take the humeral veil, and ascending the altar without attendants, after due reverence, will take the ostensorium in his hands, which are covered with the extremity of the humeral veil, and with it will give the benediction to the people; and having replaced the Blessed Sacrament on the corporal, will descend, and remain on his knees in his place. The deacon, or a priest with stole, will immediately, after due reverence, enclose the Blessed Sacrament in the tabernacle". This Instructio has been explained by Cavalieri, Tetamo, and Gardellini, who thus express themselves—
"Sacerdos", says Cavalieri (t. iv., c. ix.), "ascendit ... ad altare, et ibi, facta genuflexione unico genu accipit in manibus coöpertis per ejusdem veli extremitates ostensorium.... Quando sacerdos ascendit ut supra altare, una cum eo ascendunt itidem sacri ministri, sed hi genuflectunt postea in ore suppedanei, ubi inclinati elevant pluvialis fimbrias dum sacerdos benedicit populum. In defectu autem ministrorum sacrorum id praestant sacerdos adjutor et caeremoniarius, vel alii clerici hinc inde genuflexi.... Celebrans data benedictione ... super corporale Sacramentum collocat ... et deinde facta genuflexione unico genu, descendit cum subdiacono ad infimum altaris gradum, ubi iterum cum eodem genuflexus, per eumdem subdiaconum, vel caeremoniarium exuitur velo humerali. Diaconus interim accedit ad altare, et facta genuflexione unico genu, tabernaculum aperit et in eo reponit Sacramentum, cui genuflexione iterum facta, surgens ostiolum claudit et postea descendit ad locum suum, ad quem cum accesserit, surgunt omnes.... Quod si ultra sacros ministros adsistat sacerdos alter, hic imposita sibi stola Sacramentum ut supra recondet, et diaconus cum celebrante pariter descendet, et ab eo removebit velum humerale".
Tetamo (Append., e. iii., n. 48 et 49) thus speaks:
"Sacerdos ascendit ad altare, et ibi facta genuflexione unico genu, ut expeditius surgat, accipit in manibus coöpertis per ejusdem veli extremitates, ostensorium.... Benedicit.... Quando sacerdos ascendit, ut supra, altare, una cum eo ascendunt itidem sacri ministri, sed hi genuflectunt postea in ore suppedanei, ubi inclinati elevant pluvialis fimbrias, dum sacerdos benedicit populum; in defectu autem ministrorum sacrorum, id praestant sacerdos adjutor et caeremoniarius, vel alii clerici hinc inde genuflexi. Celebrans, data benedictione ... super corporale Sacramentum collocat".
Gardellini (n. 12 et 13), in his commentary, writes:
"Quando autem sacerdos ascendit ad altare, cum eo ascendunt etiam sacri ministri, sed hi genuflectere debent in ore suppedanei, ubi inclinati elevant pluvialis fimbrias, dum sacerdos benedicit populum.... Celebrans, data benedictione ... collocat super corporale Sacramentum ...; et deinde, facta prius genuflexione, descendit cum subdiacono ad infimum altaris gradum, ubi genuflexi ambo manent, amoto interim velo a celebrantis humeris a subdiacono, vel ut alii malunt, a caeremoniario. Interea diaconus remanens in suppedaneo altaris, reponit Sacramentum in tabernaculo, factis ante et post debitis genuflexionibus.... Quamvis vero deceat et congruat hoc munus per diaconum expleri, non est tamen necessario per eum implendum: potest alter sacerdos cum superpelliceo et stola hoc fungi munere, ideirco instructio ait: Il diacono, o un sacerdote con stola, quemadmodum fieri debet in aliis expositionibus, in quibus non parantur ministri sacri".