“A bow signifies reverence and honor shown to the persons themselves or to the signs that represent them. There are two kinds of bow: a bow of the head and a bow of the body.
“a) A bow of the head is made when the three Divine Persons are named together and at the names of Jesus, of the Blessed Virgin Mary, and of the Saint in whose honor Mass is being celebrated.
“b) A bow of the body, that is to say, a profound bow, is made to the altar; during the prayers Munda cor meum (Cleanse my heart) and In spiritu humilitatis (With humble spirit); in the Creed at the words et incarnatus est (and by the Holy Spirit . . . and became man); in the Roman Canon at the Supplices te rogamus (In humble prayer we ask you, almighty God). The same kind of bow is made by the Deacon when he asks for a blessing before the proclamation of the Gospel. In addition, the Priest bows slightly as he pronounces the words of the Lord at the Consecration.”
Why Does The Priest Break The Host During The Holy Mass?
The Structure and Meaning of The Holy Mass.
Introduction to The Holy Mass.