Śatapatha Brāhmaṇa ("of a hundred paths") 8.3.3.4

8.3.3.4

yadveva dvādaśa-dvādaśa | dvādaśākṣarā vai jagatī paśavo vai jagatyannam paśavo madhyam madhyamā citirmadhyatastadanna dadhāti tā anantarhitāḥ prāṇabhṛdbhya upadadhātyanantarhitaṃ tatprāṇebhyo 'nnaṃ dadhātyuttarā uttaraṃ tatprāṇebhyo 'nnaṃ dadhāti

And, again, why (he lays them down) by twelves,--the Gagatî consists of twelve syllables, and the Gagatî is cattle, and cattle is food, and the middlemost layer is the middle: he thus places food in the middle. He places them so as not to be separated from the Prânabhrits: he thus places the food so as not to be separated from the vital airs subsequently (to them he places them): he thus bestows food after (bestowing) the vital airs.