Shatapatha Brahmana 8.7.4.19

8.7.4.19

athādhyātmam | yaiveyam pratiṣṭhā yaścāyamavāṅ prāṇassatprathamā citirmāṃsam purīṣaṃ yatprathamāṃ citim purīṣeṇa pracādayatyetasya tadātmano māṃsaiḥ saṃcādayatīṣṭakā upadhāyāsthīṣṭakā asthi tanmāṃsaiḥ saṃcādayati nādhastātsaṃcādayati tasmādime prāṇā adhastādasaṃcannā upariṣṭāttu pracādayatyetadasya tadātmana upariṣṭānmāṃsaiḥ saṃcādayati tasmādasyaitadātmana upariṣṭānmāṃsaiḥ saṃcannaṃ nāvakāśate

Now, as to the Self (body). The first layer is the legs, and the downward flowing vital air; and the filling of soil is the flesh: thus, in covering the first layer with a filling of soil, he covers that (part) of his (Agni's) body with flesh. [He does so] after laying down bricks, and bricks mean bone: he thus covers the bone with flesh. He does not cover (the altar-site) below (the first layer), whence these vital airs are not closed up below; but, he covers it above, and thereby covers that (part) of his body above with flesh; and hence that (part) of his body above, being covered with flesh, is not visible.