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Myomorpha (cohort Glires, order Rodentia) A suborder that comprises nine families of rodents, in which the median portion of the masseter muscle runs through the infra-orbital foramen and both superficial and median parts of the masseter are inserted on the face. If present, premolars are small and are shed early in life. The families in the suborder probably are not closely related, the grouping being based on superficial characteristics. The suborder includes the rats, mice, voles, hamsters, dormice, etc.