Śatapatha Brāhmaṇa ("of a hundred paths") 8.4.2.16

8.4.2.16

yadvevaite atropadadhāti | prajāpatireṣo 'gniḥ saṃvatsara u prajāpatistasya yadūrdhvam madhyādavācīnaṃ śīrṣṇastadasyaiṣā caturthī citistadvasya hemanta ṛtustadyadete atropadadhāti yadevāsyaite ātmanastadasminnetatpratidadhāti tasmādete atropadadhāti

And, again, as to why he places these two in this (layer),--this Agni is Pragâpati, and Pragâpati is the year: what (part) of him there is above the waist, and below the head, that is this fourth layer, and that is the winter-season of him (or, of it, the year). And when he places these two in this (layer), he thereby restores to him what part of his body these two (constitute). This is why he places these two in this (layer).