GREGORY: FISH SKULLS 



283 



below and of the ethmoid region above has been that in the zanclids, acanthurids and 

 balistids the palatine, pterygoid, quadrate and metapterygoid found themselves still small 

 and delicate and in harmony with the requirements of the minute mouth, although displaced 

 so far forward that now even the metapterygoid and the adductor mandibulae muscles lay 



Fig. 161. Balistes carolintnsis. 



below and in front of the eye. Meanwhile in the zanclids the premaxilla, by reducing its 

 ascending process, became able to turn upward, while in Xesurus (Fig. 157) the dentary 

 developed a sliding connection with the articular so that it could turn downward at a 

 sharp angle, thus enabling a small mouth to open very widely without loss of biting power. 

 In all these forms, including the balistids, the lateral ethmoids have remained with 

 the orbits in a relatively posterior position while the mesethmoid has grown forward, along 

 with the parasphenoid, for the support of the snout. This is well shown in the detailed 

 topographic descriptions of the ethmoid region by Starks {\926a) who called attention to 

 the extreme anterior position of the mesethmoid in these forms. 



