OUR FACE FROM FISH TO MAN 



to the higher vertebrates, but three of which 

 (preraaxilla, maxilla, dentary) persist even in man 

 (Fig. 50). 



All these highly predatory adaptations were 

 transmitted by heredity to the oldest known 

 amphibians of the Coal Measures, which are at 

 the very least rather close relatives if not actual 

 descendants of the osteolepid crossopts. The 

 chief advance in these oldest amphibians is the 

 elimination (Fig. 17) of the whole series of plates 

 connected with the opercular tract and consisting 

 of the plates named operculum, suboperculum, 

 interoperculum, preoperculum, and a series of 

 small lateral gulars or branchiostegals. All these 

 were sacrificed when the amphibians eliminated the 

 internal gills in the adult stage. 



The loss of these plates not only constitutes a 

 fine example of Williston's law of the progressive 

 reduction in the number of bony elements, as we 

 pass from fish to man, but also serves to bring out 

 the fact that evolution proceeds fully as much by 

 the loss of superfluous parts as by the further 

 differentiation of those that remain (Figs. 50, 52). 



Many of the amphibians adopted the easy 



method of lying in wait in the water for their prey, 



114 



