Hands, do what you're bid
Bring the balloon of the mind
That bellies and drags in the wind
Into its narrow shed.
... and the extrasyllabic middle two lines bulge out suggestively, like the balloon. There ought to be a specific name for this rhetorical trick: a sort of formal meta-onomatopœia. (The off-rhyme, or sight-rhyme, mind/wind plays its part too). The narrow shed is the skull of course, and the balloon, filled with its spiritual hot-air, is the material brain matter, splodgeing and squishing like a jellyfish (why else do squid have such a pedigree in science fiction as icons of thinking aliens?) But what's particularly nice here is the way in which Yeats implies that hands trump thoughts. Homo sapiens is a handling animal before s/he is a pondering animal.