Shatapatha Brahmana 8.1.3.10

8.1.3.10

atha yā madhya upadadhāti | sa prāṇastā retaḥsicorvelayopadadhāti pṛṣṭayo vai retaḥsicau madhyamu pṛṣṭayo madhyata evāsminnetatprāṇaṃ dadhāti sarvata upadadhāti sarvata evāsminnetatprāṇaṃ dadhātyatho evaṃ haiṣa gudaḥ prāṇaḥ samantaṃ nābhim paryakno nūcīśca tiraścīścopadadhāti tasmādime 'nvañcaśca tiryañcaścātmanprāṇāḥ saṃspṛṣṭā upadadhāti prāṇānevaitatsaṃtanoti saṃdadhāti tasmādime prāṇāḥ saṃtatāḥ saṃhitāḥ

And those (bricks) which he lays down in the centre are the vital air; he lays them down on the range of the two Retahsik (bricks), for the retahsik are the ribs, and the ribs are the middle: he thus lays the vital air into him (Agni and the Sacrificer) in the very middle (of the body). On every side he lays down (the central bricks): in every part he thus lays vital air into him; and in the same way indeed that intestinal breath (channel) is turned all round the navel. He lays them down both lengthwise and crosswise, whence there are here in the body (channels of) the vital airs both lengthwise and crosswise. He lays them down touching each other: he thereby makes these vital airs continuous and connects them; whence these (channels of the) vital airs are continuous and connected.