I will instruct thee and teach thee in the way which thou shalt go: I will guide thee with mine eye. Be ye not as the horse, or as the mule, which have no understanding: whose mouth must be held in with bit and bridle, lest they come near unto thee.

-Bible (Old Testament)
Psalms 32:8^9.

He turn'd him right and round about, Upon the Irish shore, And gae his bridle reins a shake, With, Adieu for evermore, my dear, And Adieu for evermore!

-Burns, Robert
  'It was a' for our rightfu' king', stanza 3.

Perspective is the bridle and rudder of painting.

-Leonardo daVinci
Quoted in Irma  A Richter (ed) Selections from the Notebooks of Leonardo da Vinci (1977).

Nought so of love this looser dame did skill, But as a coal to kindle fleshly flame, Giving the bridle to her wanton will, And treading underfoot her honest name.

-Spenser, Edmund
  Of Malecasta.The Faerie Queen, bk.3, canto1, stanza 50.