Shatapatha Brahmana 7.1.1.18

7.1.1.18

sa catasraḥ prācīrupadadhāti | dve paścāttiraścyau dve purastāttadyāścatasraḥ prācīrupadadhāti sa ātmā tadyattāścatasro bhavanti caturvidho hyayamātmātha ye paścātte sakthyau ye purastāttau bāhū yatra vā ātmā tadeva śiraḥ

He puts on (the circular site) four (bricks) running eastwards; two behind running crosswise (from south to north), and two (such) in front. Now the four which he puts on running eastwards are the body; and as to there being four of these, it is because this body (of ours) consists, of four parts. The two at the back then are the thighs; and the two in front the arms; and where the body is that (includes) the head.