The Philosophy of the Upanishads c11.s2.t2.31

c11.s2.t2.31

The seven so-called openings of the head have undoubtedly been the starting-point for the original enumeration of the organs of sense, as is clear from the fact that in the texts of the older Upanishads only speech, breath (smell), eye, ear and manas as a fifth are usually named as organs of sense (prāṇas).⁷ Where the number is fewer, special reasons are generally present, as in Bṛih. 3. 1. 3–6, where the number four is found, or Chând. 3. 13. 5, 5. 23. 2, where the surprising omissions are perhaps to be explained by the fact that smell was supposed to be already included in the five prāṇas.⁸ Where more than five organs are named the additions are usually appended to, or even made to precede the original speech, breath, eye, ear, manas. Thus in Bṛih. 2. 5. 1–7 (s'arīram, retas), 3. 2.