Śatapatha Brāhmaṇa ("of a hundred paths") 11.5.2.4

11.5.2.4

mukhamevāsyānīkavatīṣṭiḥ mukhaṃ hi prāṇānāmanīkamuraḥ sāṃtapanīyorasā hi samiva tapyata udaraṃ gṛhamedhīyā pratiṣṭhā vā udaram pratiṣṭhityā eva śiśnānyevāsya kraiḍinaṃ haviḥ śiśnairhi krīḍatīvāyamevāvāṅ prāṇa ādityeṣṭiḥ

The offering to (Agni) Anîkavat (of the Sâkamedhâh), doubtless, is his (Pragâpati's) mouth, for the mouth is the extreme end (anîka) of the vital airs; the Sâmtapanîyâ (pap) is the chest, for by the chest one is, as it were, confined (sam-tap); the Grihamedhîyâ (pap) is the belly--to serve as a foundation, for the belly is a foundation; the Kraidina oblation is the male organ, for it is therewith that (man) sports (krîd), as it were; and the offering to Aditi is this downward breathing.