Śatapatha Brāhmaṇa ("of a hundred paths") 8.6.2.14

8.6.2.14

yoniḥ purīṣavatī | te saṃsoṛṣṭe upadadhāti saṃspṛṣṭe hyudaraṃ ca yoniśca purīśasaṃhite bhavato māṃsaṃ vai purīṣam māṃsena vā udaraṃ ca yoniśca saṃhite pūrvāticandā bhavatyaparā purīṣavatyuttaraṃ hyudaramadharā yoniḥ

A (brick) covered with loose soil is the womb. These two he lays close to each other, for the belly and the womb are close to each other. They are connected with loose soil, for loose soil means flesh, and both the belly and the womb are connected with flesh. The former is an Atikhandas, the latter a soil-bedded one (purîshavatî), for the belly is higher, and the womb lower.