Shatapatha Brahmana 10.4.1.17

10.4.1.17

tadvai lometi dve akṣare tvagiti dve asṛgiti dve meda iti dve māṃsamiti dve snāveti dve asthīti dve majjeti dve tāḥ ṣoḍaśa kalā atha ya etadantareṇa prāṇaḥ saṃcarati sa eva saptadaśaḥ prajāpatiḥ

And 'loma (hair)' is two syllables, 'tvak (skin)' two, 'asrik (blood)' two, 'medas (fat)' two, 'mâmsam (flesh)' two, 'snâva (sinew)' two, 'asthi (bone)' two, 'maggâ (marrow) ' two,--that makes sixteen digits; and the vital air which circulates therein, is the seventeenfold Pragâpati.