Śatapatha Brāhmaṇa ("of a hundred paths") 13.2.5

Pragâpati poured forth the life-sap of the horse (asva-medha); when poured forth it went from him. Having become fivefold it entered the year, and they (the five parts) became those half-months. He followed it up by means of the fifteenfold (sets of victims), and found it; and having found it, he took possession of it by means of the fifteenfold ones; for, indeed, they--to wit, the fifteenfold (sets)--are a symbol of the half-months, and when he seizes the fifteenfold ones, it is the half-months the Sacrificer thereby takes possession of.

Concerning this they say, 'But, surely, the year is not taken possession of by him who spreads out (performs sacrifice for) a year in any other way than by means of the Seasonal sacrifices.' The Seasonal sacrifices, doubtless, are manifestly the year; and when he seizes the Seasonal victims, he then manifestly takes possession of the year. ‘And, assuredly, he who spreads out the year in any other way than with the (victims) of the set of eleven (stakes) is deprived of his offspring (or subjects) and cattle, and fails to reach heaven. This set of eleven (stakes), indeed, is just heaven, and the set of eleven (stakes) means offspring (or people) and cattle and when he lays hands on the (victims) of the (two) sets of eleven (stakes) he does not fail to reach heaven, and is not deprived of his offspring and cattle.

Pragâpati created the Virâg; when created, it went away from him, and entered the horse meet for sacrifice. He followed it up with sets of ten (beasts). He found it, and, having found it, he took possession of it by means of the sets of ten: when he seizes the sets of eleven (beasts), the Sacrificer thereby takes possession. of the Virâg. He seizes a hundred, for man has a life of a hundred (years) and a hundred energies: vital power and energy, vigour, he thus takes to himself.

Eleven decades he seizes, for the Trishtubh consists of eleven syllables, and the Trishtubh means energy, vigour: thus it is for the obtainment of energy, vigour. Eleven decades he seizes, for in an animal there are ten vital airs, and the body: (trunk) is the eleventh: he thus supplies the animals with vital airs. They belong to all the gods for the completeness of the horse (sacrifice), for the horse belongs to all the gods. They are of many forms, whence beasts are of many forms; they are of distinct forms, whence beasts are of distinct forms.