In Through the Vanishing Point (44) McLuhan cites from W.B. Yeats’ Byzantium (1928):

The unpurged images of day recede;
The Emperor’s drunken soldiery are abed;
Night resonance recedes, night walkers’ song
After great cathedral gong;
A starlit or a moonlit dome disdains
All that man is,
All mere complexities,
The fury and the mire of human veins.

It is on the other side of this night (“now that my ladder’s gone”) where (indeed, also when) the “midden heap” — aka “language itself” — is to be found.  Here is “where all the ladders start”:

Those masterful images because complete
Grew in pure mind, but out of what began?
A mound of refuse or the sweepings of a street,
Old kettles, old bottles, and a broken can,
Old iron, old bones, old rags, that raving slut
Who keeps the till. Now that my ladder’s gone,
I must lie down where all the ladders start,
In the foul rag-and-bone shop of the heart.

McLuhan cited these lines from Yeats’ The Circus Animals’ Desertion (1938) over and over again in his late texts: in Take Today, in ‘Man as the Medium’ (the introduction to his 1976 commentary on Sorel Etrog’s film, Spiral) and, especially, in From Cliché to Archetype where they are cited twice, along with the first lines of the poem:

I sought a theme and sought for it in vain,
I sought it daily for six weeks or so.
Maybe at last, being but a broken man,
I must be satisfied with my heart, although
Winter and summer till old age began
My circus animals were all on show,
Those stilted boys, that burnished chariot,
Lion and woman and the Lord knows what.¹