Śatapatha Brāhmaṇa ("of a hundred paths") 3.8.3.2

3.8.3.2

atha yadvapayā pracarya | etena puroḍāśena pracarati madhyato vā imāṃ vapāmutkhidanti madhyata evainametena medhena samardhayati kṛtsnaṃ karoti tasmādvapayā pracaryaitena puroḍāśena pracaratyeṣa nvevaitasya bandhuryatra kva caiṣa paśum puroḍāśo 'nunirupyate

And why he proceeds with that cake after performing (offering) with the omentum is this. It is from the middle (of the victim) that this omentum is pulled out, and from the middle he now completes that (victim) by means of that sacrificial essence and makes it whole; therefore he proceeds with that cake after performing with the omentum. The relation of this (cake to the animal offering), indeed, is one and the same everywhere; that cake is prepared after (and supplementary to) a victim.