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THE POPULAR SCIENCE MONTHLY. 



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 when- 



FlG. l. 



Dog approaching another Dog with Hostile Intentions. (By M. Riviere.) 



ever 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 fascise of 

 the frontal muscle. These latter fascise draw up the inner ends of the 

 eyebrows, and wrinkle the forehead in the peculiar manner which we 

 immediately recognize as the expression of gi-ief or anxiety. Laugh- 

 ter and tears form media of expression, which have been often sub- 

 jected 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 



