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lip. ( 1 of an embryonic BLASTOPORE) the rim of the blastopore. ( 2 of a flower perianth) a group of perianth segments united to a greater or lesser extent, to form a distinct grouping thus divided from the rest of the perianth. ( 3 of vertebrates) one of two fleshy parts (upper and lower) surrounding the mouth.
Lips are the structure which covers the opening of the mouth and consists of the upper and the lower lips. Each of the lip is surrounded by the orbicularis oris muscle which encircles its opening.[1] Lip twitching is the sudden abnormal involuntary contractions of the lip muscles. It may sometimes involve the upper, lower or both the lips together. It might be due to some direct stimulation or due to irritation of the nerve supplying the muscles surrounding the lips.