This is Jock (also known as Spug!) Muir. Jock never competed in the TT - only in the Manx, every year from 1930 to 1933 inclusive. His best result was the '31 Senior win, on a Norton. He also came second in '32 on a Velo in the Junior and 5th in the Senior on a Velo in 1930. In '33 he rode a 350 Norton as well and finished 13th on it.