This is copied after a drawing by John Ruskin in his Rudimentary Series. See "Catalogue of the Rudimentary Series: in the arrangement of 1873 with Ruskin's comments of 1878," Lion and Unicorn Press, London, 1984. It appears as no. R47, reproduced in b/w p. 68, text p. 69: "Sketch of head of living Lion. A really good sketch of my own which may serve to show that I could have done something if I had not had books to write. It is to be copied by all advanced students as an exercise in fast pencil drawing."
