EVOLUTIOX OF THE Ili'MAN FACE 



370 



of tlie fislilikc vcrtelinitcs, that we sec 

 the vertebrate face in its typical rm-iii 

 and that we see all the elements which 

 are characteristic of the face of maiii- 

 mals. p]ven the familiar lamliiiarks ol' 

 the human face are all })resent. W'c 

 have the nostrils, which are only in- 

 definitely foreshadowed in earlier types ; 

 we have the e3'es, the mouth, the 

 tongue, and the lips. But in the shark 



teeth of vci'tchi-atcs lias had a ,L;iTat 

 inihience upon the t'volut ion of the 

 fa CO. 



in the shark the face is vci-y dis- 

 tinctly the directing part of the animal, 

 at the front end of the backbone. We 

 may say that all the elaborate locomo- 

 tive organs (the backbone, the fins, and 

 the muscles which move them) exist 

 chiefly for the purpose of bringing the 



In .sharks we see for the first time the vertebrate face in typical form, with all the elements of the 

 face of man — mouth, tongue, and lips to he brought into contact with the food by the locomotive organs, 

 and noi-trils and eyes to direct the locomotiv(> organs. In the frilled shark {('lilniiijidi).srlarhus) figured 

 we see a suggestion of how teeth were formed in the higher vertebrates. The teeth within the .shark's 

 mouth are enlarged shagreen denticles such as grow on the skin outside the mouth. Aflrr (lannaii 



the whole face is covered with a tough 

 skin. 



In certain sharks {Chhuiiijiloscld- 

 cJiiis) we see a suggestion as to how 

 the teeth were formed in higher verte- 

 brates. The tough skin, covering the 

 head and body, is everywhere thickly 

 studded with minute teeth, or denticles, 

 the whole forming the "shagreen" of 

 commerce. Xow the teeth in the .shark's 

 mouth are nothing but enlarged sha- 

 green denticles. At the sides of the 

 mouth the denticles gradually become 

 larger and the skin that bears them be- 

 comes drawn over the margins and on 

 to the inner side of the jaws. I need 

 hardly say that the evolution of the 



mouth into contact with the food, and 

 that the higher elements of the face, 

 namely the eyes and the nose, exist for 

 the purpose of directing the locomotive 

 apparatus toward the ])rey. In order to 

 consume the food and transform its ])0- 

 tential energy into action, the shark 

 must of course have oxygen, which 

 among fishes is extracted by the Idood 

 from the water surrounding the gills. 

 These gills are supported by cartilagi- 

 nous arches M'hich are of the greatest 

 importance in the later evolution of the 

 face, since there is good evidence tend- 

 ing to show that the upper and lower 

 halves of one of these gill arches actu- 

 ally gave rise to the upper and lower 



