Shatapatha Brahmana 9.3.1.22

9.3.1.22

atha yaṃ tṛtīya dakṣiṇato juhoti | prāṇāḥ sa sa saptakapālo bhavati sapta hi śīrṣanprāṇāstamanantarhitam pūrvasmājjuhotyanantarhitāṃstacīrṣṇaḥ prāṇāndadhāti

And the third (cake) which he offers on the right side, is the vital airs; it is one of seven potsherds, for there are seven vital airs in the head. He offers it close to the preceding one: he thus puts the vital airs so as to be close to (not separated from) the head.