GREGORY: FISH SKULLS 



421 



A raising of the point Q (with shortening of QQ') will decrease the angle of the gape, as 

 in Figs. 2S7D, 286D; while a lowering of the point Q will increase the angle of the gape, as 

 in Fig. 2885, D. 



The Suspensorium. — The suspensorium of long jaws is primitively inclined backward, 



Pomacanthus^ 



Fig. 290. Progressive forward swing of the suspensorial line (HQ) with protrusion of preorbital face and reduction of 



mouth in balistoids. 



as in Cheirolepis (Fig. 286 J), so that a good part of the jaws lies behind the orbiton {0'); 

 but the teleosts appear to have been derived from small-mouthed forms (Fig. 287^^) with 

 a forwardly inclined suspensorium which, with some exceptions, retains its forward inclina- 

 tion even after the jaws become secondarily elongated, as in LefidosUus (Fig. 287D) and 



