OUR FACE FROM FISH TO MAN 



The third of the secondary jaw elements is the 

 dentary bone, one on each side of the lower jaw. 

 In the lobe-finned or crossopt fishes this bone. 



Fig. 63. Under Side of the Skull of Devonian Fossil Fish (A) 



AND Primitive Fossil Amphibian (B). (A after Bryant 



AND Watson; B after Watson). 



The secondary upper jaws are on the margins; the primary upper 

 jaws are largely covered by tooth-bearing plates of the primary palate. 

 For details, see p. xxvii. 



while bearing a stout series of teeth, had not yet 



assumed the primacy it acquired in later types. 



We have already (pages 36-39) traced its progress 



in the mammal-like reptiles and have seen it 



encroach on the other membrane bones of the 



lower jaw until it finally secured a contact with the 



108 



