Śatapatha Brāhmaṇa ("of a hundred paths") 3.8.2.20

3.8.2.20

tāmantareṇa yūpaṃ cāgniṃ ca haranti | tadyatsamayā na haranti yenānyāni havīṃṣi haranti nedaśṛtayā samayā yajñam prasajāmeti yadu bāhyena na harantyagreṇa yūpam bahirdhā yajñātkuryustasmādantareṇa yūpaṃ cāgniṃ ca haranti dakṣiṇataḥ parītya pratiprasthātā śrapayati

They take it along between the sacrificial stake and the fire. The reason why they do not take it across the middle (of the altar), where they take other sacrificial dishes, is lest they should bring the sacrifice in the middle into contact with the uncooked (omentum). And why they do not take it there outside (the altar) along the front of the sacrificial stake, is that they would thereby put it outside the sacrifice; therefore they take it along between the sacrificial stake and the fire. Having gone round to the south side, the Pratiprasthâtri roasts it.