OUR ANCIENT RELATIVES 



bones of the human skull, together with many 

 other bony elements which were reduced and 

 gradually eliminated in the long procession of 

 forms from fish to man. 



Before looking forward to man, let us look back- 

 ward and see how the skulls of these earliest 

 explorers of the land compared with those of their 

 collateral ancestors, the air-breathing, lobe-finned 

 ganoids. 



The greatest change is seen in the region of the 

 gill chamber, just behind the upper jaws. In the 

 fish this was covered by a beautifully jointed series 

 of bony plates, as perfectly articulated as any suit 

 of armor ever made by man. In the oldest 

 amphibians, however, these bony plates behind 

 the jaws have disappeared completely, leaving an 

 exposed area called the otic notch just behind the 

 upper jaw. This is the region of the middle ear 

 or sound-transmitting apparatus in modern amphi- 

 bians and apparently these ancient amphibians 

 had already acquired this new instrument of pre- 

 cision. In the lower jaw the bony plates covering 

 the under surface of the throat had also dis- 

 appeared. In the region above the nostrils the 



mosaic of small bones found in the lobe-finned 



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