The triangularis rarely pulls the mouth corner down by itself. It normally appears in the company of the mentalis, as part of the pout or the facial shrug. Because it attaches to the mouth corner at the same point as the zygomatic major, it's also the muscle we use to keep the corner down when we're trying not to smile. The triangularis fits around the chin like chinstraps. Its fixed end is sewn into the lower edge of the jaw on either side of the chin. Its free end is attached to the mouth-circling muscle (orbicularis oris) at the same point (A) where the smiling muscle, zygomatic major (B), attaches.
The triangularis is one of the two muscles that makes the mouth frown—the other is mentalis.
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