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Walk the Even Hospital Database by book and chapter — the raw source passages that ground Ask, DDx, and the rest.

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introductionstatpearls· Introduction· item NBK540999

If you are smiling right now, you are likely engaging the risorius muscle – that is, if you even have a risorius muscle. Commonly known as the smiling muscle, it serves as a muscle of facial expression. As alluded to here, it is not present in all people, and it is believed to be unique only to the Hominines, or the African great apes and humans, evolving in our common ancestor.[1]