Brihadaranyaka Upanishad, Chapter 3, Fourth Brahmana (from: http://www.swami-krishnananda.org/brdup_audio/brdup-17.pdf ) He who breathes in through the Prana is your inner Self. He who performs the function of expiration is your own Self that is working in the form of this outward breath, the Apana. That which pervades your whole body, known as Vyana, again, is the operation of your own Self. T..