“As it happens, the Herk household did have a dog, named Roger. Roger was the random result of generations of hasty, unplanned dog sex: Among other characteristics, he had the low-slung body of a beagle, the pointy ears of a German shepherd, the enthusiasm of a Labrador retriever, the stubby tail of a boxer, and the intelligence of celery.”

Hurry Home, Candy (1953)

Source: Zen and the Art of Motorcycle Maintenance (1974), Ch. 30
Source: Zen and the Art of Motorcycle Maintenance: An Inquiry Into Values

"The Designers and the Politicians" (1962), later published in Beyond Left & Right : Radical Thought for Our Times (1968) by Richard Kostelanetz, p. 368
1960s
Context: Technology paces industry, but there's a long lag in the process. Industry paces economics. It changes the tools, a great ecological change. And in that manner we come finally to everyday life.
The politician is someone who deals in man's problems of adjustment. To ask a politician to lead us is to ask the tail of a dog to lead the dog.

His collected works contain no riddle about dog legs, but George W. Julian recounts Lincoln using a similar story about a calf in Reminiscences of Abraham Lincoln by distinguished men of his time (1909), p. 241: "There are strong reasons for saying that he doubted his right to emancipate under the war power, and he doubtless meant what he said when he compared an Executive order to that effect to 'the Pope’s Bull against the comet.' In discussing the question, he used to liken the case to that of the boy who, when asked how many legs his calf would have if he called its tail a leg, replied, 'Five,' to which the prompt response was made that calling the tail a leg would not make it a leg."
A very similar riddle about cow legs was also circulated by Edward Josiah Stearns' Notes on Uncle Tom's Cabin (1853), p. 46: '"Father," said one of the rising generation to his paternal progenitor, "if I should call this cow's tail a leg, how many legs would she have?" "Why five, to be sure." "Why, no, father; would calling it a leg make it one?"'
Misattributed

Source: Trinity Coach Bob Beatty on Bobby Petrino, The Courier Journal, 8 Jan 2014, 29 May 2017, Jones, Steve http://www.courier-journal.com/story/sports/college/louisville/2014/01/08/trinity-coach-bob-beatty-on-bobby-petrino-theres-nobody-better-to-lead-louisville/4380995/,

Sophia and Luke, Chapter 4 Sophia, p. 64
2009, The Longest Ride (2013)

Source: The Vicar of Wakefield (1766), Ch. 17, An Elegy on the Death of a Mad Dog, st. 4.