Śatapatha Brāhmaṇa ("of a hundred paths") 1.2.1.2

1.2.1.2

śiro ha vā etadyajñasya yatpuroḍāśaḥ sa gānyevemāni śīrṣṇaḥ kapālānyetānyevāsya kapālāni mastiṣka eva piṣṭāni tadvā etadekamaṅgamekaṃ saha karavāva samānaṃ karavāveti tasmādvā etadubhayaṃ saha kriyate

The head of this sacrifice is (represented by) the rice-cake: for those potsherds (kapâla), no doubt, are to this (rice-cake) what the skull bones (kapâla) are to the head, and the ground rice is nothing else than the brain. Now this (combination of skull and brain) certainly forms one limb: 'Let us put that (which is) one together! Let us make it one!' thus they think; and therefore the two acts are done simultaneously.