GREGORY: FISH SKULLS 



185 



between the articular and the dentary, due to the buckling of the lower border of the 

 mandible at the junction of these two bones. The effect of the contraction of the large 

 adductor mandibulse must be to convert a long, nearly horizontal, into a strong, short 

 vertical, movement of the tooth row, while posterior dislocation of the dentary is prevented 

 by the high ascending bar of the articular. In this arrangement there is a certain re- 

 semblance to the double-jointed mandible of the parrot fishes (Fig. 134). 



B rye on dentex 



Fig. 70. Brycon dtntex. Side view. 



Gasteropelecus. — In the "fresh-water flying fish" of South America the skeleton as a 

 whole conforms to the characin type, but the opposite coracoids are enormously enlarged 

 into a fan-like keel for the support of the muscles of flight. In the excellent figure of the 

 skeleton given by Ridewood (1913, PI. XVI) the skull is seen to be compactly built and to 

 be crowded forward, so to speak, by the enormous coracoids. The mouth is small and 

 sharply upturned, but with stoutly built jaws and strong short teeth. The broad suspen- 

 sorium curves forward beneath the large orbit. The opercular is shortened vertically. 

 The skull-roof is low but strongly built. 



