614 



THE PELVIC FIN. 



longitudinal bars of their respective fins is in favour of rather 

 than against this view. The same may be said of the fact that 

 the first part of each girdle to be formed is that in the neigh- 

 bourhood of the longitudinal bar (basipterygium) of the fin, the 

 dorsal and ventral prolongations being subsequent growths. 



The later development of the skeleton of the two fins is more 

 conveniently treated separately. 



The pelvic fin. The changes in the pelvic fin are compara- 

 tively slight. The fin remains through life as a nearly horizontal 

 lateral projection of the body, and the longitudinal bar the 



FIG. 346. TRANSVERSE SECTION THROUGH THE PECTORAL FIN OF A YOUNG 



EMBRYO OF SCYLLIUM STELLARE. 

 /////. basipterygial bar (metapterygium) ; fr. fin ray; in. muscles; hf, horny fibres. 



basipterygium at its base always remains as such. It is for a 

 considerable period attached to the pelvic girdle, but eventually 

 becomes segmented from it. Of the fin rays the anterior 

 remains directly articulated with the pelvic girdle on the sepa- 

 ration of the basipterygium (fig. 347), and the remaining rays 

 finally become segmented from the basipterygium, though they 

 remain articulated with it. They also become to some extent 

 transversely segmented. The posterior end of the basipterygial 

 bar also becomes segmented off as the terminal ray. 



The pelvic fin thus retains in all essential points its primitive 

 arrangement. 



