[O.B.Left]

I asked Yoda this same question. Off the top of his head (Yoda has an amazing grasp of the derivation or "family tree" of golf knowledge)
he mentioned;

Robert MacDonald, Golf 1927.

Percy Boomer, On Learning Golf, 1946.

And provided a doff of the hat to Seymour Dunn, Golf Fundamentals, 1922. With the caveat that he attributed the straight left arm to the LEFT arm triceps.

During a similar sort of conversation he traced Big Jack's rolled over left foot back to pre Roman Scotland. Gotta love it. He must have one heck of a golf library.

O.B.