Shatapatha Brahmana 8.1.1.1

8.1.1.1

prāṇabhṛta upadadhāti | prāṇā vai prāṇabhṛtaḥ prāṇānevaitadupadadhāti tāḥ prathamāyāṃ citā upadadhāti pūrvārdha eṣo 'gneryatprathamā citiḥ purastāttatprāṇāndadhāti tasmādime purastātprāṇāḥ

He lays down the Prânabhritah (breath-holders): now, the Prânabhritah being--the vital airs, it is the vital airs he thereby bestows upon (Agni). He lays them down in the first layer;--that which is the first layer is the forepart (ground-part) of Agni: it is thus in front that he puts (into Agni) the vital airs, whence there are (in creatures) these (orifices of the) vital airs in front.