Attachments of incisivis. The incisivis originates on jawbones above and below the lip (A) and attaches to mouth corners (B). Basic action is simple: All sections act together, pulling mouth corners toward each other.
There is a muscular knot at the mouth corner thick enough to see and to feel. You can see it in three-quarter views, where it always makes a subtle extra curve at the level of the mouth (C). The knot is the group attachment of zygomatic major (D), triangularis (E), risorius (F), and several other muscles to the orbicularis oris, holding it in place. On some faces, the entire oval form of orbicularis can be sensed underneath the surface, like a section of a cone (G).
In the shouting mouth, both lips are tight and thin.
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