OUR FACE FROM FISH TO MAN 



inherited from the primitive crossopts Hes deeply 

 covered by a mobile fleshy curtain. Doubtless 

 the evolution of true lips was a part of the general 

 transformation of reptiles with unstable body 

 temperature and low grade metabolism, into 

 mammals living at high pressure. 



In an earlier chapter (pages 43, 44) it has been 

 mentioned that the facial muscles of mammals 

 represent a forward extension of a thin layer of 

 muscle covering the neck of lower vertebrates and 

 that when this muscle migrated forward beneath 

 the skin it dragged its own nerve with it, which 

 was subdivided into smaller branches as the 

 muscle itself was differentiated into the facial 

 muscles of the ears, eyes, nose and lips (Figs. 23, 

 24). The history of this invasion is now being 

 traced in convincing detail by Huber. The inva- 

 sion was facilitated by the fact that in the early 

 stages of development (Figs. 65A, 69) the region 

 of the mouth and lips arises quite close to the 

 original territory of the facial nerve, which was 

 on the side of the neck, so that forks of the parent 

 mass in the neck could easily spread to the lips 

 and forehead. 



The researches of Ruge, Huber, Sonntag and 



132 



