PROTRACTILE MOUTHS 



skull of an ordinary type and of a John Dory. At 

 the first glance their profound lack of resemblance is 

 obvious. In the former, the premaxilla, on each side, 

 is small and reasonably regular in shape. In the 



Fig. 21. — Head of a John Dory, mouth nearly closed. 



latter, the premaxilla is a large bone wedged in, so to 

 speak, showing two almost equally sized branches, one 

 vertical and upright, bordering the mouth, with the 

 maxilla behind it, the other horizontal and higher up, 

 extending backwards as far as the orbit. The vertical 

 branch is jointed at its lower extremity with the base 

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