Śatapatha Brāhmaṇa ("of a hundred paths") 8.3.4

He then lays down the Vâlakhilyâs;--the Vâlakhilyâs, doubtless, are the vital airs: it is the vital airs he thus lays (into Agni). And as to why they are called Vâlakhilyâs,--what (unploughed piece of ground lies) between two cultivated fields is called 'khila;' and these (channels of the) vital airs are separated from each other by the width of a horsehair (vâla), and because they are separated from each other by the width of a horse-hair, they (the bricks) are called Vâlakhilyâs.

He places seven in front, and seven at the back. When he places seven in front, he thereby restores to him those seven (organs of the) vital airs here in front.

And those seven which (he places) behind he thereby makes the counter-breathings to those (first breathings); and hence by means of (the channels of) these breathings he passes over the food which he eats with those (other) breathings.

And, again, as to why he places seven in front,--there are seven (channels of the) vital airs here in the front part (of the animal) --the four upper and lower parts of the fore-feet, the head, the neck, and what is above the navel that is the sixth, for in each limb there is a vital air: this makes seven vital airs here in front; it is them he thus lays into him (Agni-Pragâpati).

And as to what seven (bricks) he places behind,--there are seven vital airs here in the back part--the four thighs and knee-bones, the two feet, and what is below the navel that is the seventh, for in each limb there is a vital air: this makes seven vital airs here at the back; it is them he thus lays into him.

[He lays them down, with, Vâg. S. XIV, 21,22], 'The head thou art, the ruler! steady thou art, steadfast! a holder thou art, a hold!'--'A guider, a ruler! a guider thou art, a guide! steady thou art, a steadier!' he truly bestows steady vital airs unto him.

And, again, as to why he lays down the Vâlakhilyâs,--it was by means of the Vâlakhilyâs that the gods then ranged over these worlds, both from hence upwards and from yonder downwards; and in like manner does the sacrifice now, by means of the Vâlakhilyâs, range over these worlds, both from hence upwards and from yonder downwards.

By 'The head thou art, the ruler!' they stepped on this (terrestrial) world; by 'Steady thou art, steadfast!' on the air-world; by 'A holder thou art, a hold!' on that (heavenly) world.--'For life-strength (I bestow) thee! for vigour thee! for husbandry thee! for prosperity thee!' There are four (kinds of) four-footed (domestic) animals, and (domestic) animals are food: by means of this food, these four four-footed animals, they (the gods) established themselves in yonder world; and in like manner does the Sacrificer now by means of this food, these four four-footed animals, establish himself in yonder world.

That was, as it were, an ascent away from hence; but this (earth) is a foothold: the gods came back to this foothold; and in like manner does the Sacrificer now come back to this foothold.

By 'A guider, a ruler!' they stepped on that (heavenly) world; by 'A guider thou art, a guide!' on the air-world; by 'Steady thou art, a steadier!' on this (terrestrial) world.--'For sap (I bestow) thee! for strength thee! for wealth thee! for thrift thee!'--There are four four-footed (domestic) animals, and (domestic) animals are food: by means of this food, these four four-footed animals, they (the gods) established themselves in this world; and in like manner does the Sacrificer, by means of this food, these four four-footed animals, establish himself in this world.

Now as to the restoration (of Pragâpati-Agni). Those eleven bricks he lays down, which (constitute) that first anuvâka, are the air and this body (of Agni, the altar). And as to why there are eleven of these, it is because the Trishtubh consists of eleven syllables, and the air is of the trishtubh nature. And the sixty subsequent (bricks) are Vâyu, Pragâpati, Agni, the Sacrificer.

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.

And those which he places on the right (south) side are that (part) of him which is above the waist and below the head. And those at the back are that (part) of him which is above the feet and below the waist. Those on the left (north) side are the feet themselves.

And the seven (Vâlakhilyâs) which he places in front are these seven vital airs here in the forepart (of an animal): it is these he thus puts into him (Agni). He places them so as not to he separated from those ten (Prânabhrits): he thereby puts in vital airs that are not separate from the head.

And the seven he places at the back (of the altar) are those seven vital airs behind: it is these he thereby puts into him. He places them so as not to be separated from those twelve (Khandasyâs): he thereby puts into him vital airs that are not separate from the body. That same Vâyu-Pragâpati is turned round in all directions in this trishtubh-like air; and when he lays down the third layer, having made up both Vâyu (the wind) and the air, he thereby adds them to himself. He then puts down two Lokamprinâ (space-filling bricks) in that corner: the significance of them (will be explained) further on. He throws loose earth (on the layer): the significance of this (will be explained) further on.