Origin of the Shield Shape in the Solar Folio of the f85-86 Foldout

[Dobri]

While trying to find a proper name for the 'O'-shaped shield frame in the solar folio of the f85-86 foldout,
I came across the following description concerning You are not allowed to view links. Register or Login to view.: 

"Clergy have used less-military shapes such as the oval cartouche, but the shield has always been a clerical option. Clergy in Italy often use a shield shaped like a horse's face-armor."