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BNF Français 343 Queste del Saint Graal Tristan de Léonois 39r 1380
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BCUL U 964 Biblia Porta North France 006v 1300
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5'8" rider on a 13.2 hand mule
Mules are the hybrid offspring of mares (female horses) and jacks (male donkeys). Mules are seen extensively in medieval art seeing service as both ridden and working animals.
Their longs ears and full tails mark them as mules. Donkeys have a more switch like tail with minimal hair on the fleshy part and a poof of longer hair towards the bottom. Horses have short ears.
Mules were drawn with various levels of quality. Humble mules pull plows and carry packs. Finer mules serve as palfreys wearing fine tack and carrying high ranking persons including noble men and Kings.
The written record:
Mules have a prominent place in the pictorial record and are referenced in inventory accounts. They are well regarded. However, mules are not mentioned in any of the horsemanship specific treatises that I have read. Those treatises tend to focus on war animals and reference others by breed type.
I have identified a 15th century Italian translation of a 5th century Latin veterinary treatise that specifically mentions mules and donkeys - "L'arte de la Medicina de les Bestie". Scans of an extent copy are available online, but I have not yet explored it in depth.
I have found and additional reference to a 15th Century Iberian Treatise with a volume on mules but have not yet found a copy.