Brihadaranyaka Upanishad 4.2.3

4.2.3

athaitadvāme'kṣaṇi puruṣarūpameṣāsya patnī virāṭtayoreṣa sam̐stāvo ya eṣo'ntarhṛdaya ākāśo'thainayoretadannaṃ ya eṣo'ntarhṛdaye lohitapiṇdo'thainayoretatprāvaraṇāṃ yadetadantarhṛdaye jālakamivāthainayoreṣā sṛtiḥ saṃcaraṇī yaiṣā hṛdayādūrdhvā nāḍyu-ccarati yathā keśaḥ sahasradhā bhinna evamasyaitā hitā nāma nāḍyo'ntarhṛdaye pratiṣṭhitā bhavantyetābhirvā etadāsravadāsravati tasmādeṣa praviviktāhāratara ivaiva bhavatyasmācchārīrādātmanaḥ

'Now that which in the shape of a person is in the right eye, is his wife, Virâg. Their meeting-place is the ether within the heart, and their food the red lump within the heart. Again, their covering is that which is like net-work within the heart, and the road on which they move (from sleep to waking) is the artery that rises upwards from the heart. Like a hair divided into a thousand parts, so are the veins of it, which are called Hita, placed firmly within the heart. Through these indeed that (food) flows on flowing, and he (the Taigasa) receives as it were purer food than the corporeal Self (the Vaisvânara).