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Mesaxonia (infraclass Eutheria, cohort Ferungulata) A superorder that comprises the one order, Perissodactyla, of those extant and extinct ungulates in which the third digit bears most of the weight of the animal, the other digits being reduced. The name is derived from the Greek mesos, ‘middle’, and axon, ‘axis’. It has recently been proposed that the Hyracoidea also belong to the Mesaxonia.