Bowing the Head at Hearing the Holy Name
The custom of bowing the head at the mention of His Name was formally written into law at the Second Council of Lyons, A.D. 1274, convened by Pope Gregory X:
"Those who assemble in church should extol with an act of special reverence that Name which is above every Name, than which no other under Heaven has been given to people, in which believers must be saved, the Name, that is, of Jesus Christ, Who will save His people from their sins. Each should fulfill in himself that which is written for all, that at the Name of Jesus every knee should bow; whenever that glorious Name is recalled, especially during the sacred Mysteries of the Mass, everyone should bow the knees of his heart, which he can do even by a bow of his head."
O Divine Jesus, Thou hast promised that anything we ask of the Eternal Father in Thy name shall be granted.
O Eternal Father, in the name of Jesus, for the love of Jesus, in fulfillment of this promise, and because Jesus has said it, grant us our petitions for the sake of Jesus, Thy Divine Son. Amen.
Source: The Prayer Book by Reverend John P. O'Connell, M.A., S.T.D. and Jex Martin, M.A., The Catholic Press, Inc., Chicago, Illinois, 1954