Śatapatha Brāhmaṇa ("of a hundred paths") 8.7.2.10

8.7.2.10

ubhayīryajuṣmatīśca lokampṛṇāścātmannupadadhāti | tasmādayamātmā dviguṇo bahulatara iva lokampṛṇā eva pakṣapuceṣu tasmātpakṣapucāni tanīyāṃsīvānūcīśca tiraścītmannupadadhātyasthīni vā iṣṭakāstasmādimānyanvañci ca tiryañci cātmannasthīni parācīreva pakṣapuceṣu na hi kiṃ cana pakṣapuceṣu tiryagasthyasti taddhaitadeva citasya cācitasya ca vijñānamevameva cita itarathācitaḥ

On the body (of the altar) he places both (bricks) possessed of formulas and Lokamprinâs; whence that body (of a bird) is, as it were, twice as thick. On the wings and tail (he places) only Lokamprinâs, whence the wings and tail are, as it were, thinner. On the body (of the altar) he places them both lengthwise and crosswise, for the bricks are bones: hence these bones in the body run both lengthwise and crosswise. On the wings and tail (he places them so as to be) turned away (from the body), for in the wings and tail there is not a single transverse bone. And this, indeed, is the difference between a built and an unbuilt (altar): suchlike is the built one, different therefrom the unbuilt one.