Śatapatha Brāhmaṇa ("of a hundred paths") 6.3.1.28

6.3.1.28

te prāñcastiṣṭhanti | aśvaḥ prathamo 'tha rāsabho 'thāja evaṃ hyete 'nupūrvaṃ yadvai tadaśru sakṣaritamāsīdeṣa so 'śvo 'tha yattadarasadivaiṣa rāsabho 'tha yaḥ sa kapāle raso lipta āsīdeṣa so 'jo 'tha yattatkapālamāsīdeṣā sā mṛdyāmetadāhariṣyanto bhavantyetebhyo vā eṣa rūpebhyo 'gre 'sṛjyata tebhya evainametajjanayati

They (the animals) stand facing the east, first the horse, then the ass, then the he-goat; for this is their proper order. For that horse (asva) is the tear (asru) which there (at the creation) formed itself; and that ass (râsabha) is that which, as it were, cried (ras); and that he-goat (aga, unborn) is the juice which adhered to the shell; and that clay which they are about to fetch is nothing else than the shell (of the egg): for it was from these forms that he was created at first, and from them he thus produces him.