galea salutis

From Rev. Henry McCloud’s Clerical Dress and Insignia of the Roman Catholic Church, pages sixty-six through seventy-two: How the Biretta is worn and removed

The biretta is worn squarely upon the head, neither tilted over the right or left ear. The peakless side is worn over the left ear. The biretta may be worn only when sitting, or when walking outside the church. The biretta is of obligation for those dressed in sacred vestments, and they alone may wear it when walking within the church.The biretta is put on after the cleric is seated and removed before he rises. In putting on or removing the biretta from the head the middle peak, never the front peak, is taken between the index and the middle fingers of the right hand.When seated if the biretta is removed for a few moments it is held in the right ahnd and rested upon the right knee.    

Carrying and presenting the biretta

In procession or while standing the biretta is held in front of the breast, having both thumbs inside at the bottom of the biretta and the hand joined beneath.The biretta is presented to the celebrant by holding it so that the middle peak is nearest to him and the peakless side the furthest from him.   

Liturgical Uses

The biretta is prescribed to be worn by the celebrant, and in solemn Masses by the deacon and the subdeacon in going to the altar and returning to the sacristy.When the celebrant and the sacred ministers, and also the clergy sit during the Mass they wear their biretta unless the Blessed Sacrament is exposed. They remove their birettas at the parts of the Gloria and Credo and at the other times prescribed by the rubrics.The wearing of the biretta in choir is not of strict obligation. But for uniformit where it is the local custom to wear the biretta in choir then everyone should wear it during the recitation of the psalms and canticles.Seminarians often, from custom, wear their biretta while at meals.   

Biretta may be used

The biretta may be used while preaching, hearing confessions, and at the exorcisms at baptism.   

Biretta is not used

The biretta may not be used when the Blessed Sacrament is exposed or veiled during a sermon; in processions of the Blessed Sacrament or of the true cross; in other processions while within the church exceot by those in sacred vestments; in church outside of the sacred functions; while kneeling or standing, excet while preaching or at the exorcisms baptism; by a bishop while wasking his hands for private Mass; by a bishop when wears sacred vestments, but if the bishop vests in the sacristy it seems permissible for him to wear the biretta in going to the altar and returning to the sacristy; by the master of ceremonies, nor by the cross bearer even when in the vestments of a subdeacon, acolytes, and canopy bearers.   

Other occasions

The biretta may be worn with the cassock outside of sacred functions. In this case it is removed to greet a superior or to an equal whom the wearer wishes to honor, but never to an inferior.