Śatapatha Brāhmaṇa ("of a hundred paths") 8.7.3.4

8.7.3.4

svayamātṛṇāyāmopya | anūkyayā saṃcādayannetyā pariśridbhyaḥ sa tenaiva dakṣiṇāvṛjjaghanena svayamātṛṇāṃ saṃcādayannaityā punaranūkyāyai

Having strewed it on the svayamâtrinnâ (place) he goes on covering (the altar) from the (brick) on the cross-spine up to the enclosing-stones. In the same way he goes on covering it from left to right behind the naturally-perforated one up to the one on the cross-spine again.