OUR FACE FROM FISH TO MAN 



teeth below the ostracoderm grade of evolution. 

 But when we reach the grade of evolution repre- 

 sented by the shark, we find that the shark stands 

 unquestionably nearer to man in the construction of 

 its jaws and teeth than it does to any known group of 

 invertebrates; while between shark and man many 

 intermediate conditions of the mouth are definitely 

 known. 



THE PRIMARY JAWS 



The gill pouches of fishes and of the embryos of 

 higher vertebrates, including man, are supported 

 by cartilaginous bars (Figs. 7, 8), the so-called 

 "visceral arches," and the mouth pouches of 

 sharks and embryo vertebrates are likewise sup- 

 ported by cartilaginous bars, the oral cartilages, 

 which have every appearance of belonging in 

 series with the gill arches. The primary upper 

 jaw cartilages, one on either side, are called the 

 palatoquadrate cartilages, while the primary lower 

 jaw cartilages are called Meckel's cartilages, or the 

 mandible. The "labial cartilages" in front of 

 the jaws (Figs. 7, 8) are possible remnants of at 

 least one "premandibular" arch. 



In the predecessors of the sharks, we may infer, 



102 



