EVOLUTIOX OF THE HUMAN FACE 



383 



fact p'ives tlic eluu ^ to tliu origin <»l' tlu' 

 facial muscles. In the remote ancestors 

 of the mammals only the ])latysma and 

 the immediately nnderlying sphincter 

 colli muscles were present; it is highly 

 prol)ahle that this sheet of nerve tissue 

 gradually spread froui the under side 

 of the throat upward and foi-ward 



' Tlieory put forth by Ruge. Tliis is generally 

 accepted by anatomists as the true explanation of 

 the origin of the facial muscles of mammals. 



along the sides of the face, hy degrees 

 creeping over the old bony mask and 

 beneath the skin, carrying with it the 

 seventh nerve, and dividing and sub- 

 dividing into numerous branches and 

 layers; at the same time the nerve 

 branched and branched again, as nerves 

 have frequently been known to do when 

 muscles became subdivided. Several 

 analogous cases of the spread of a mus- 

 cle laver into a new region are known 



The photograph shows the tense lips of a trained chimpanzee \\\,<> i- i;, ihe act of threading a needle. 

 The action of the muscles of the human face is coordinated (especially in the child) with that of various 

 other muscles of the body, and the same is noticeable in apes, which use the facial muscles much as we 

 do but often with rather more empliasis than is usual in polite society. Courtesy of Professor W. T. Shep- 

 herd, of Washington, D. C. 



