        “Our ancestors used to count in fours,” Luna proclaimed.  “This was the primary hoof, this the second, this the third, and this the fourth.”  She lifted each hoof in turn.  “Unicorns found this unsatisfactory, and came up with a tripartite hoof model—the interior heel, exterior heel, and the toe.  We and our sister mandated that system be used exclusively forthwith, although some more rustic enclaves of Earth Pony society still insist on using the quarter system, despite its obvious limitations.  Some evidence of it lingers yet, such as the four cardinal points.”