Śatapatha Brāhmaṇa ("of a hundred paths") 6.2.1.11

6.2.1.11

tadyāstāḥ śriyaḥ | etāni tāni paśuśīrṣāṇyatha yāni tāni kusindhānyetāstāḥ pañca citayastadyatpaśuśīrṣāṇyupadhāya citīścinotyetaireva tacīrṣabhiretāni kusindhāni saṃdadhāti

As to those glories, they are these same heads of the victims; and those (headless) trunks are these five layers (of the fire-altar): thus when he builds up the layers after putting on the heads of the victims, he thereby unites those trunks with those heads.