Śatapatha Brāhmaṇa ("of a hundred paths") 9.2.3.46

9.2.3.46

tiṣṭhantsamidha ādadhāti | asthīni vai samidhastiṣṭhantīva vā asthīnyāsīna āhutīrjuhoti māṃsāni vā āhutaya āsata iva vai māṃsānyantarāḥ samidho bhavanti bāhyā āhutayo 'ntarāṇi hyasthīni bāhyāni māṃsāni

Standing he puts on the logs,--the logs are bones, and bones stand, so to speak. Sitting he offers the oblations,--oblations are the flesh, and the flesh sits (lies), so to speak. The logs are inside (the fire), and the oblations outside, for the bones are inside, and the flesh is outside.