Natyashastra
अङ्गान्येतानि चत्वारि सर्वेष्वासारितेष्विह । उपोहनं मुखं तेषां युग्मं प्रतिमुखं भवेत् ॥ ८६॥
These four limbs are present in all Āsāritas. The Upohana corresponds to the Mukha, and the Yugma corresponds to the Pratimukha.
english translation
aGgAnyetAni catvAri sarveSvAsAriteSviha । upohanaM mukhaM teSAM yugmaM pratimukhaM bhavet ॥ 86॥
hk transliteration by Sanscript