OUR ANCIENT RELATIVES 



All these muscles, like those of the locomotor 

 apparatus, are composed of striped muscle fibers 

 and each little fiber is a sort of engine, deriving its 

 fuel from the chemical glycogen in the blood 

 and its explosive impulse from a tiny nerve 

 fiber. 



Over the whole of this great complex is stretched 

 a tough but flexible envelope, the skin, which is 

 studded with minute teeth, or shagreen. 



Around the jaw-bars the shagreen gives rise to 

 large teeth. 



Thus in barest outline we have the elements of 

 the face and its connections with the braincase 

 in the shark. If we are fond of mysticism we will 

 say that in the cramped brain-box lives the shark 

 himself, who receives the multitudinous messages 

 from his detecting instruments and shapes his 

 actions accordingly. In this anthropocentric phil- 

 osophy a shark's face is highly expressive of the 

 shark's piratical and cruel character. If we wish 

 to be thoroughly behavioristic, on the other hand, 

 we will regard the shark's conduct as the automatic 

 resultant of the various stimuli received by his 

 sensorium, which were transmitted to the complex 



apparatus in the central nervous system, the office 



19 



