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TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



jaws, so that predaceous jaws and habits become more pronounced. Meanwhile, the rela- 

 tive size of the orbits decrease rapidly, the jaw muscles increase so that, as noted above, the 

 opercular fold is displaced backward. 



i 



pf&paretti 



ddti.. 



A Pomatomus 



Centropoma c RstLilarta 



Fig. 294. Differential lengthening of parts of the neurocranium. A. Normal percoid. B. Elongate percoid. C. Excessive 



elongation of preorbital face. 



At first (Fig. 292) the vertical diameter of the brain is greater than that of the future 

 back and the myomeres are very small, especially in the vertical diameter. In many 

 teleosts, however, the myomeres grow rapidly in the vertical direction, adding an extra V 



