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. 



