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Frontal view of a rabbit with the lips retracted by a gloved hand, showing the shallow grooves in the enamel of the incisors (arrows) used for measurement of eruption rate. Two grooves are visible on every tooth except the mandibular right incisor, which has only 1. The more coronal groove on the mandibular left incisor's edge is almost worn away. New grooves were placed every several days as the old ones wore off.
