246 



FISHES 



CHAP. VIII 



PTG 



Teleostei, but even these may be absent, and the dermal fin-rays 

 then articulate directly with the basipterygium. Little is known of 

 the skeleton of the pelvic fins in the fossil Crossopterygii, but there 

 is evidence of the existence of a higher 

 grade of structure than in their surviving 

 allies. In Eustkenopteron^ for example, 

 the fin is supported by an axis of at least 

 three bony segments, with at least three 

 ossified preaxial radialia ; hence, it has 

 obviously undergone less degeneration than 

 in Polypterus, where the fin -skeleton is 

 essentially Teleostean. In the Dipnoi the 

 pelvic fins are similar to the correspond- 

 ing pectoral fins, but individual variation 

 is more marked and even the central 

 axis may divide. 2 In the males of all 

 existing Elasmobranchs, including the 

 Holocephali, certain of the more distally 



FIG. 149. Skeleton of the situated metapterygial radialia become 

 left pelvic fin of a Trout mo( }ined to form a supporting skeleton 



(Salmo fano), seen from 



the dorsal surface. B.PTG, for the copulatory organs, the claspers, 



2STff%fplS or mixipterygia. I* the latter group 

 distal radialia. (From the anterior claspers are also provided 

 with cartilaginous supports articulating 

 with the pelvic girdle directly in front of the pelvic fins. 



1 Traquair, Geol. Mag. vii. 1890, p. 15 ; Goodrich, I.e. 

 2 Haswell, Proc. Linn. Soc. N.S. W. ix. 1884, p. 71 ; Howes, P.Z.S. 1887, p. 3. 



