Maestro dell'Osservanza aka Sano di Pietro's Santo Giorgio

Salve,
 back to the XV century art and portrayal of the riding equipment.
In this Gothic painting we have a curb-bit, full horse horse harness and typical knightly war saddle of the period.

it is San Giorgio (Saint George) and the dragon from the Provenzano  Museo Diocesano in Siena, Italia.
Painted by the master of  the Observance Triptych, lately determined to be a painter of the Sienese School Sano di Pietro.

dextrarius opertus - gray war charger, with free flowing mane and tail, with  feathered fetlocks

large-shanked curb-bit, the bridle has no browband, otherwise it is dyed vivd red and studded with metal buttons (gold?)

the breastplate has the heraldic device in the center- the Saint George coat of arms

gilded stirrups & gilded long rowel spurs

I wonder if the way the Saint-knight is holding the bridle reins - palm downwards, only fingers are holding the loose rein -   may indicate that this is the XV century depiction of neck-reining method and we see here a horse trained in neck-reining?

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