Natyashastra
आयामनादुभयतः पाश्वयोः स्यात् प्रसारितम् । परिवर्तात्रिकस्यापि विवर्तितमिहेष्यते ॥ २३९॥
The sides are stretched outward in both directions, and the turning of the Trika (sacrum) is also considered as Vivartita in this context.
english translation
AyAmanAdubhayataH pAzvayoH syAt prasAritam । parivartAtrikasyApi vivartitamiheSyate ॥ 239॥
hk transliteration by Sanscript