The.Skull 115 



and, from their rod-like jointed character, they look 

 very much like the real gill-arches of a fish. The fourth 

 arch vanishes. 



Such is the almost incredible alchemy which Nature 

 has wrought from a plastic rod of gristle, transforming 

 it into beak, tongue, and ears. Few of us, when watch- 



FIG. 89. Ultimate distribution of the four embryonic gill-arches in the skull 

 of the adult bird. The dotted portions are not developed. (Adapted from 

 Newton.) Compare with Figs. 83 and 88. 



ing the gently waving gills of a fish, have realized how 

 much we indirectly owe to them. A noted German 

 anatomist Karl Gegenbaur believes that we owe even 

 our hands and arms (by way of the pectoral fins of fishes) 

 to portions of the gill framework, but this theory is not 

 generally accepted. 



