The Vedanta Sutras, commentary by Sankaracharya (SBE34), tr. by George Thibaut  at sacred-texts.com
31. On the ground of imaginative identification (the highest Lord may be called prâdesamâtra), Gaimini thinks; for thus (Scripture) declares.
Or else the passage about him who is measured by a span may be considered to rest on imaginative combination.--Why?--Because the passage of the Vâgasaneyi-brâhmana
which treats of the same topic identifies heaven, earth, and so on--which are the members of Vaisvânara viewed as the Self of the threefold world--with certain parts of the human frame, viz. the parts comprised between the upper part of the head and the chin, and thus declares the imaginative identity of Vaisvânara with something whose measure is a span. There we read, 'The Gods indeed reached him, knowing him as measured by a span as it were. Now I will declare them (his members) to you so as to identify him (the Vaisvânara) with that whose measure is a span; thus he said. Pointing to the upper part of the head he said: This is what stands above (i.e. the heavenly world) as Vaisvânara (i.e. the head of Vaisvânara 1). Pointing to the eyes he said: This is he with good light (i.e. the sun) as Vaisvânara (i.e. the eye of V.). Pointing to the nose he said: This is he who moves on manifold paths (i.e. the air) as Vaisvânara (i.e. the breath of V.). Pointing to the space (ether) within his mouth he said: This is the full one (i.e. the ether) as Vaisvânara. Pointing to the saliva within his mouth he said: This is wealth as Vaisvânara (i.e. the water in the bladder of V.). Pointing to the chin he said: This is the base as Vaisvânara (i.e. the feet of V.).'--Although in the Vâgasaneyi-brâhmana the heaven is denoted as that which has the attribute of standing above and the sun as that which has the attribute of good light, while in the Khândogya the heaven is spoken of as having good light and the sun as being multiform; still this difference does not interfere (with the unity of the vidyâ) 2, because both texts equally use the term 'measured by a span,' and because all sâkhâs intimate the same.--The above explanation of the term 'measured by a span,' which rests on imaginative identification, the teacher Gaimini considers the most appropriate one.
152:1 Atra sarvatra vaisvânarasabdas tadangaparah. Go. Ân.
152:2 Which unity entitles us to use the passage from the Sat. Brâ. for the explanation of the passage from the Kh. Up.