OUR FACE FROM FISH TO MAN 



supplanted them, at least in the tooth-bearing 

 regions. In mammals (including man) clear traces 

 of the primary upper jaw may be found in early 

 embryonic stages of development (see Keith, 

 Human Embryology and Morphology, 1921, pages 

 138, 148, 172). 



THE RISE OF THE SECONDARY JAWS AND 

 THEIR TEETH 



Up to the present time we have been dealing 



with the origin and early evolution of the primary 



upper and lower jaws, but in the higher vertebrates, 



including man, these primary jaws are completely 



overshadowed and masked by the secondary jaws. 



In the sharks the secondary jaws are represented 



merely by the skin that is wrapped around the 



primary jaws, or palatoquadrate and Meckel's 



cartilage, both on the outside and on the inside of 



the mouth. In the sharks this skin has no bony 



base but in the higher fishes and early amphibians 



the primary upper and lower jaws are covered 



with many-layered bony plates originally provided 



with a porcelain-like surface of "ganoine" and 



usually bearing numerous teeth. In the early 



lobe-finned, air-breathing fishes (Figs. 11, 12) 



106 



