ANATOMICAL STEUCTUEE OF ANTHEOPOID APES. 157 



seriously ill, the expression of their eyes is often 

 most affecting. 



The forehead of these animals is frequently 

 marked by transverse furrows, and especially, as 

 Darwin justly observes, when they raise their eye- 

 brows. The same great observer considers that the 

 countenances of anthropoids are, in comparison with 

 those of men, generally inexpressive, and indeed, 

 chiefly in consequence of the fact that they do not 

 wrinkle the forehead when they are excited. The 

 wrinkling of the forehead, which is one of the most 

 significant forms of expression in man, is due to 

 the action of the corrugatores supercilii, by which 

 the eyebrows are drawn down and closer to each 

 other, so as to form vertical folds on the forehead. 

 It has been asserted that the orang and chim- 

 panzee possess these muscles, but they seem to be 

 rarely exercised — at any rate, to any remarkable 

 extent.* When Darwin brought a chimpanzee 

 out of his dark chamber into bright sunshine, 

 he only once observed a slight wrinkling of the 

 forehead. When the same observer tickled the 

 nose of a chimpanzee with a straw, its face was 

 slightly wrinkled, and faint vertical furrows appeared 

 between the eyebrows.f Darwin never observed any 

 wrinkling of the forehead in an orang. I myself 

 have observed a contraction of that region of the 



* Maoalister, in the Annals and Magazine of Natural History, 

 vii. 342 (1871) asserts that he was unable to distinguish the 

 oorrugator from the orbicular muscle, and I have been equally 

 unsuccessful. 



t Darwin's Expression of the Emotions. 



