Śatapatha Brāhmaṇa ("of a hundred paths") 8.6.2.15

8.6.2.15

te prācyā upadadhāti | prāṅ hyeṣo 'gniścīyate 'tho prāgvai prāca udaram prācī yonirbahistomabhāgaṃ hṛdayaṃ vai stomabhāgā hṛdayamu vā uttamathodaramatha yoniḥ

He places them so as to extend eastwards, for in an easterly direction this Agni (fire-altar) is built; and, moreover, in one moving forward, both the belly and the womb are moving forward. Outside the Stomabhâgâs (he places them), for the Stomabhâgâs are the heart, and the heart is highest, then (comes) the belly, then the womb.