Bhashya
अथास्या ऊरू विहापयति 'विजिहीथां द्यावापृथिवी' इत्यनेन ।तस्यामर्थमित्यादि पूर्ववत् ।त्रिः एनां शिरःप्रभृति अनुलोमामनुमार्ष्टि 'विष्णुर्योनिं' इत्यादि प्रतिमन्त्रम् ॥
In plain words
'He parts her thighs' — that is done with the mantra 'let heaven and earth open.' 'He settles himself in her' and the rest follow exactly as already explained. He strokes her three times, starting at the head and moving with the hair, saying 'may Viṣṇu shape the womb' and the rest of that formula, one line for each stroke.
Close to the Sanskrit
'Then he causes her two thighs to part' — by this [mantra] 'let heaven and earth separate.' 'Having settled the organ in her' and so on [is understood] as before. He strokes her thrice, starting from the head, along the grain of the hair, [with] 'may Viṣṇu prepare the womb' and so on, mantra by mantra.