Page:Popular Science Monthly Volume 2.djvu/454

438 brow is drawn up under this emotion, the forehead being contracted or wrinkled at the same time. Mr. Darwin evolves the origin of this involuntary movement, through the same logical train of sequence by which we have seen him, in his earlier and more elaborate works, draw out the extraordinarily complex chain of laws, which runs through natural history. When infants scream loudly from hunger or pain, the circulation is affected, and the eyes tend to become gorged with blood. In consequence, the muscles surrounding the eyes are strongly contracted by an involuntary action as a protection. This action, in the course of many generations, has become firmly fixed and inherited. With advancing years and culture, the habit of screaming is partially repressed; but the muscles round the eyes still tend to contract whenever



even slight distress is felt. Of these the pyramidal muscles of the nose are less under the control of the will than the others, and their contraction can be checked only by that of the central fasciae of the frontal muscle. These latter fasciæ draw up the inner ends of the eyebrows, and wrinkle the forehead in the peculiar manner which we immediately recognize as the expression of grief or anxiety. Laughter and tears form media of expression, which have been often subjected to analysis, but never with the same physiological minuteness and precision as in Mr. Darwin's special chapters on the phenomena of the vaso-muscular and nervous systems. The excess of nervous