Vṛṣṇivaṃśa–Anukīrtana (Enumeration of the Vṛṣṇi Lineage) — Questions on Viṣṇu’s Human Descent
अपानः पश्चिमं कायमु दानो ऽर्द्धं शरीरिणः / व्यानो व्यानीयते येन समानः सर्वसंधिषु
apānaḥ paścimaṃ kāyamu dāno 'rddhaṃ śarīriṇaḥ / vyāno vyānīyate yena samānaḥ sarvasaṃdhiṣu
Apāna abides in the body’s western/back region; udāna in half of the embodied being; vyāna is that by which the movement is carried everywhere; and samāna dwells in all the joints.