There is actually a model horse available (Anatomy in Motion) that has the skeleton on one side and the musculature on the other. It is based on the project that these 2 women take a grey horse (like the one in the picture), spend around 4 hours painting him (skeleton/muscle) then lunge him (walk, trot, and canter) so you can see it all. There are videos of this available in addition to videos where one is riding the horse and she is wearing a skeleton costume.
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http://www.modelhorses.com/bentley/traditionalmodels_accessories/fanatasy_series/images/1228_large.jpg (from the Bentley Model Horse site www.modelhorses.com/bentley)s