Communion on the tongue is an Apostolic tradition
Statements from Popes, Saints and Church Councils:
St. Sixtus 1 (circa 115): “The Sacred Vessels are not to be handled by others than those consecrated to the Lord.”
St. Basil the Great, Doctor of the Church (330-379): “The right to receive Holy Communion in the hand is permitted only in times of persecution.” St. Basil the Great considered Communion in the hand so irregular that he did not hesitate to consider it a grave fault.
The Council of Saragossa (380): Excommunicated anyone who dared continue receiving Holy Communion by hand. This was confirmed by the Synod of Toledo.
The Synod of Rouen (650): Condemned Communion in the hand to halt widespread abuses that occurred from this practice, and as a safeguard against sacrilege.
6th Ecumenical Council, at Constantinople (680-681): Forbade the faithful to take the Sacred Host in their hand, threatening transgressors with excommunication.
St. Thomas Aquinas (1225-1274): “Out of reverence towards this Sacrament [the Holy Eucharist], nothing touches it, but what is consecrated; hence the corporal and the chalice are consecrated, and likewise the priest’s hands, for touching this Sacrament.” (Summa Theologica, Part III, Q. 82, Art. 3, Rep. Obj. 8.)
The Council of Trent (1545-1565): “The fact that only the priest gives Holy Communion with his consecrated hands is an Apostolic Tradition.”
Pope Paul VI (1963-1978): “This method [on the tongue] must be retained.” (Memoriale Domini)
Pope John Paul II: “To touch the sacred species and to distribute them with their own hands is a privilege of the ordained.” (Dominicae Cenae, 11)