Gifford calls here’s my head and my heels are coming "a popular expression suggesting ill-coordinated haste of a person whose intentions are better than his performance." Documentary evidence shows it is rather a person’s figure and posture than their attitude that is indicated here.
A possible, though slightly uncertain early candidate can be found in a New Zealand paper:
When our local friend discovers that he has collided, he stands still, here’s my head fashion, and in a very gentlemanly manner politely intimates to the butcher, that he is waiting to pass […]
Marlborough Express (Blenheim, New Zealand) 24 February 1877, p. 7
and the first available example of the full form again comes from the New Zealand papers:
Who is that delicate-looking youth with the "Here’s my head, and my feet are coming" expression, that invariably appears in Volunteer uniform at the various dances held in town?
New Zealand Observer 4 August 1883, p. 18
Whereas the first two examples leave the reader guessing the meaning of the expression, the following quotation clearly indicates that it relates to a forward-stooping posture:
Sit up straight in your saddle, Simpson. It's “here's my head and my boots are coming” with you — sit upright, man. I saw you in the Park on Saturday, on foot, with Ada. You'll never be able to take her out for a ride if you don't learn to ride better than that.
H. P. Holt, The Mounted Police of Natal (London 1913), p. 21
Other evidence suggests that the tendency of tall people to stoop may be another component in the meaning of the phrase:
The science of Anthropology has divided mankind into two main branches, the Long and the Short Heads. We all of us know the sort of Image that when it enters a room says as plainly as any Ideograph, "'Ere's my 'ead, and my hinder parts (Exodus 33, v. 23) are coming". If the creature were examined it would be found to be dolichocephalic and steatopygous.
The New Age (1915), vol. 16, p. 573
and Joyce’s friend Byrne confirms this in his memoir when writing about a Dublin librarian, Tommy Hickey:
He was so tall, and so conscious of it, that he always walked stooped forward. Of course, he couldn't escape being joked about as "here's me head, and me heels are comin'".
J.F. Byrne, Silent Years (New York 1953), p. 21
Eric Partridge, in his Dictionary of Slang and Unconventional English (1937) offers a more colourful version of the expression:
"here’s me head, me arse is comin'", which he says was “a workmen's c[atch]p[hrase]., dating since c. 1895 […] in ref. to a girl or woman that, wearing high heels, walks with the shoulders well forward and with the buttocks (esp. if shapely or buxom) well behind. Orig[inally] of any forward-slooping person”.
There is no doubt that this version was established, as it was used years later by Frank McCourt:
That's where poor Peter Dooley comes in. We call him Quasimodo because he has a hump on his back like the one on the hunchback of Notre Dame […] Before he leaves his house he always sticks his head out the door and tells the lane, Here's me head, me arse is coming.
Frank McCourt, Angela’s Ashes (New York, 1996), p.188
and Partridge’s nuance is seen in this quotation, from the same year as Partridge’s dictionary:
She has a large posterior which sticks out so that she has a suggestion of "here's my head and my backside is coming" about her when she walks across a room.
Rearden Conner, A Plain Tale from the Bogs (London 1937), p. 96
But this feature of the phrase does not seem to be relevant to the I-narrator of the Cyclops episode when he scoffs at Bloom as a cattle dealer’s assistant busily scribbling in his notebook.
Finally, we can see that numerous slang sites, such as Irish Identity, attest to the use of the phrase in contemporary Hiberno-English.
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