Śatapatha Brāhmaṇa ("of a hundred paths") 8.3.4.12

8.3.4.12

tadyāḥ purastādupadadhāti | śiro 'sya tāstā daśa bhavanti daśa vai prāṇāḥ prāṇā u vai śiraḥ pūrvārdha upadadhāti purastāddhīdaṃ śiraḥ

Those which he places in front are his head: there are ten of them, because there are ten vital airs, and the head is (the focus of) the vital airs. He places them in front, because the head (of an animal) is here in front.