48 



PROF. T. H. HUXLEY ON CERATODUS FORSTERI. [Jan. 4, 



has undergone a twist, the direction of its rotation is exactly contrary 

 to that which has occurred in the fish. Taking the left limb in each 

 case, the normal fin would have to be turned in the direction of move- 

 ment of the hands of a watch to bring it to the teleostean position, 



Fig. 10. 



Pr.a 



POL YODON 



The left pectoral fins of Ceratodus forsteri, Notidanus cinereus (foetal), Scyllium 

 canicula, Chim&ra monstrosa, and Polyodon folium. 



The prseaxial (Pr.a) and postaxial (Pf.o) margins of all are turned in the same 

 direction ; 2?, the prseaxial ray (propterygium of Gegenbaur) ; 3ft, the 

 metapterygiuni ; I, the basal or proximal joint of the axial skeleton. 



while it would have to be turned in the contrary way to bring it into 

 the amphibian position. Hence the praeaxial edge in the teleostean 

 fin is dorsal, while in the amphibian limb it is more or less ventral ; 



