And Izzzzz has (unwittingly?) answered question #3:
It was not until well into the twentieth century that the far reaches of Queens, southeast Brooklyn, the north Bronx, and Staten Island were fully urbanized, and at that point the cylce had to return to Manhattan. In this way, the heraldic emblem of the city has changed from the image of a thermometer to the image of the worm Ouroboros, its tail forever in its mouth.
—Luc Sante, Low Life
(NB, this quote contains a clue to the BONUS QUESTION!)
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Answer to ouroboric question #1:
(Unfortunately I can't find a bigger image — it's Harry Crews's novel A FEAST OF SNAKES. It's the only Crews I've read...I read it for the cover!)