Verse 3.8

आदित्यो ह वै बाह्यः प्राण उदयत्येष ह्येनं चाक्शुषं प्राणमनुगृह्णानः । पृथिव्यां या देवता सैषा पुरुषस्यअपानमवष्टभ्यान्तरा यदाकाशः स समानो वायुर्व्यानः ॥ ८ ॥

ādityo ha vai bāhyaḥ prāṇa udayatyeṣa hyenaṃ cākśuṣaṃ prāṇamanugṛhṇānaḥ | pṛthivyāṃ yā devatā saiṣā puruṣasyaapānamavaṣṭabhyāntarā yadākāśaḥ sa samāno vāyurvyānaḥ || 8 ||

8. The sun, indeed, is the external prana. He rises favouring the prana in the eye. So the goddess of the earth attracts the apana downwards. The akasa between is samana. The wind is vyana.

Shankara’s Commentary:

Com.—The sun is the well-known outward Prana among the Devas. He rises and by his light favours this prana, lodged in the eye of the body, i.e., helps it with luminosity in the perception of forms. Similarly the well-known goddess presiding over earth, attracts or controls the activity of the apana in the purusha and favours its action by pulling downwards; for, otherwise, this body, owing to its weight, may fall down, or being unimpeded, may fly up. The air in the akasa, in the middle, i.e., between the earth and heaven (by the word akasa, the wind in it is denoted, as those in a cot are denoted by the word cot) is samana, i.e., favours samana, samana resembling it, in the fact of being enclosed within the akasa in the middle. The external wind, vayu, generally because it resembles vyana in pervading, favours vyana. This is the drift.