Mayamatam 12.81

12.81

rajatena paśuṃ vidyāccaturdikṣuvinikṣipet
madhye gopuṅgavaṃ caivatannirīkṣya yugaṃ punaḥ

one should know an animal of silver and place [them] in the four directions; / and a bull in the center, looking toward the yoke;