Darwin made one of his few mistakes when he included among rudimentary and inherited structures[48] those few long hairs which are often seen in the eyebrows of man, looking upon them as representatives of those found in some species of macacus and the chimpanzee. That great and modest man was, I am sure, not in the habit of making much use of the looking-glass--not more than women who, as we know, rarely do such a thing. But if he did he would have observed in his own splendid frontal region and brows excellent examples of the phenomena which form the subject of this chapter. This I know, though I never saw him in the flesh, for it so happens that in the great volume published in the jubilee of The Origin, and called _Darwin and Modern Science_, two good photographs of him, at the ages of thirty-five and about seventy-one are reproduced. These both show, but the later one much more clearly, good examples of these long and not very ornamental aberrant hairs. Thirty-five years of arduous thought and work had told their tale on him and twisted from their normal paths the lengthening thickening hairs of his eyebrows. [48] _Descent of Man_, p. 19. Also, if he had looked a little beyond the eyebrows he would have seen some very deep wrinkles of the skin on his forehead and round his orbits. It is these two groups of facts, wrinkles and twisted, changed hairs of man’s eyebrows, which give the answer to the question “Can muscular action change the direction of hair in the individual?” In 1903 I drew the attention of the Anatomical Society of Great Britain and Ireland to these two groups of facts under the title “Notes on the Eyebrows of Man,” and presented some large drawings of individual elderly men of my acquaintance, and the present chapter is only an extension of that little piece of work. No area of the mammalian skin is so useful and easy to follow as this in answering the present question, for though the previous chapter supplied part of the answer in a very fruitful field, the proof still remained one of “tremendous probability” and not more. But in the frontal and superciliary region of man there is complete proof of the truth of the affirmative answer, as I shall show.