Natyashastra
प्राकृतं शेषभावेषु गण्डकर्म भवेदिति । विवर्तनं कम्पनं च विसर्गो विनिगूहनम्॥१४२॥
Sama (natural)—in the remaining conditions. Gestures of the lips are six in number. (They are): Vivartana (narrowing), Kampana (trembling), Visarga (spreading out), Vinigūhana (concealing).
english translation
prAkRtaM zeSabhAveSu gaNDakarma bhavediti । vivartanaM kampanaM ca visargo vinigUhanam॥142॥
hk transliteration by Sanscript