Shatapatha Brahmana 6.4.1.6

6.4.1.6

athainaṃ kṛṣṇājine sambharati | yajñā vai kṛṣṇājinaṃ yajñaevainametatsambharati lomataścandāṃsi vai lomāni candaḥsvevainametatsambharati tattūṣṇīmupastṛṇāti yajño vai kṛṣṇājinam prajāpatirvai yajño 'nirukto vai prajāpatiruttaratastasyopari bandhuḥ prācīnagrīve taddhi devatrā

He then deposits it upon the black antelope skin, for the black antelope skin is the sacrifice: in the sacrifice he thus deposits it (or him, Agni);--on the hair (side); for the hair is the metres: he thus deposits him on the metres. That (skin) he spreads silently; for the black antelope skin is the sacrifice; and the sacrifice is Pragâpati, and undefined is Pragâpati. North (of the hole he spreads it),--the meaning of this (will be explained) hereafter;--on (the skin spread) with the neck-part in front, for thus (it is turned) towards the gods.