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WordNet
mandibular notch

n. small indentation in the middle of the lower jawbone

Wikipedia
Mandibular notch

The upper border of the ramus of mandible is thin, and is surmounted by two processes, the coronoid process anteriorly and the condyloid process posteriorly, separated by a deep concavity, the mandibular notch, or sigmoid notch. It allows the passage of the masseteric nerve (a branch of the mandibular nerve (V3) division of the trigeminal nerve), masseteric artery and masseteric vein.