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lip
One of two fleshy folds around the entrance to the mouth. Externally the lips are covered with skin and internally with mucous membrane, the relative transparency of which allows the red-pink of the underlying capillaries to show through.
The main substructure of the lips is a ring of muscle, whose functions including keeping food in the mouth, helping to produce speech and other sounds (whistling, for example), and kissing. Smaller muscles at the corners of the lips are responsible for facial expression.
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