Such a mitre appears on a seal of Archbisho p Thomas Becket (Father Thurston, The ?P allium, London, 1892, p. 17), The custom was, however, .already growing up of setting the horns over the front and back of the head instead of the sides (the mitre said to have belonged to St Thomas Becket, now at Westminster Cathedral, is of this type), 1 and with this the essential character of the mitre, as it persisted through the middle ages, was established.
Thurston, The Stations of the Cross (London, 1906).
Father Thurston traces it to a combination in the i 6th and 17th centuries of customs that had their origin in the 13th, i.e.
" Blessing," by P. Morrisroe, and "Benediction of the Blessed Sacrament," by Herbert Thurston, S.J.; in all of which further authorities are cited.
The authority to grant such discharge was conceived to be included in the power of binding and loosing committed by Christ to His Church; and when in the course of time the vaguer theological conceptions of the first ages of Christianity assumed scientific form and shape at the hands of the Schoolmen, the doctrine came to prevail that this discharge of the sinner's debt was made through an application to the offender of what was called the " Treasure of the Church " (Thurston, p. 315).