Natyashastra
इति दन्तोष्ठजिह्वानां करणाच्चिबुकक्रिया । विधुतं विनिवृत्तं च निर्भुग्नं भुग्नमेव च ॥ १५४॥
So much about the gestures of the chin in relation to the teeth, the lips and the tongue. Gestures of the mouth are: Vidhuta, Vinivṛtta, Nirbhugna, Bhugna,
english translation
iti dantoSThajihvAnAM karaNAccibukakriyA । vidhutaM vinivRttaM ca nirbhugnaM bhugnameva ca ॥ 154॥
hk transliteration by Sanscript