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1. that part of the oral cavity proper, on each side of the frenulum of the tongue, between the tongue and the mandibular alveolar process or ridge;
2. in the embryo, the groove on each side between the lingual primordium and the alveolar elevations of the mandible.
The space in the floor of the mouth between the base of the tongue and the alveolar ridge, on each side extending from the frenum of the tongue back to the retromolar wall.
See also: sulcus