OUR FACE FROM FISH TO MAN 



none of these "visceral arches" (labial cartilages, 

 jaws or gill arches) were connected with the brain- 

 case except by connective tissue and as the living 

 prey was presumably small there was no need of 

 special bracing for these arches. But as the race 

 grew larger the size of the prey likewise increased 

 and convulsive swallowing efforts were made by 

 the fish to force the prey past the region of the gill 

 pouches down into the stomach. At the same 

 time the contractile muscles around the whole 

 branchial series grew stronger, those attached to 

 the future jaw arches increased faster than their 

 fellows and so did the future jaws themselves. 

 In this way the jaw muscles of the shark and of 

 higher vertebrates (Fig. 61) were apparently 

 derived by enlargement from muscles correspond- 

 ing to the constrictor muscles of the gill arches. 



For a long time the primary upper jaw was 

 suspended from the skull mainly through its 

 attachment to the second or hyoid arch (Fig. 62A) 

 but in the amphibians and higher vertebrates the 

 primary upper jaw itself becomes attached to the 

 skull (Fig. 62, B, C). When large tooth-bearing 

 bony plates came to sheath and cover over the 



primary upper and lower jaws they gradually 



104 



