GREGORY: FISH SKULLS 



293 



In this family i,Fig. 170) the opposite halves of both beaks have fused together into 

 an unusually broad, massive beak, which now serves the double function of cutting and 

 crushing. Secondary shortening of the muzzle has now gone so far, however, that the 

 mesethmoid is very short anteroposteriorly. 



Diodon 



Fig. 171. Diodon hyilrix. Top view. 



Support for the massive beak is given by the greatly enlarged palatine, whose hammer 

 usurps the place of the vestigial prefrontal. There is a marked secondary enlargement 

 of the metapterygoid, quadrate and hyomandibular. In the top view (Fig. 171) the skull 

 is extremely wide and short. 



