302 



A CTINOP TER YG1I 



Division 4. 

 ACTINOPTBRYGII. 



The paired fins are non-lobate, the radials having been so much 

 reduced that they scarcely project beyond the body-wall, and the 



web of the fin is almost 

 entirely supported by 

 the dermotrichia. The 

 same is the case in the 

 median fins. It cannot 

 be said that there is any 

 evidence of a biserial 

 arrangement of the 

 radials in the paired fins 

 of the Actinopterygii, 

 yet it is usually sup- 

 posed that they have 

 FIQ 276 been derived from such 



Ventral view of the cartTlaginous skeleton of the pelvic archipterygium by 



girdle and fin of Sca-phirhynchus. (After Rautenfeld.) the lOSS OI the post-axil 



Pm, median, and Pd, dorsal process of girdle; }F, nerve- j- i /r{ nn i M KQ 



foramen ; 1-9, radials. radials (tjrCgenbaur [158, 



162], Braus [48]; see 



p. 108). All distinct trace of an axis has disappeared in the pelvic 

 fin of the Holostei, 

 where the few remain- 

 ing radials articulate 

 directly with the pelvic 

 bone (Figs. 245 - 8). 

 This is also the case 

 Avith the pectoral fin 

 of the Teleostei (Figs. 

 243,480). Butin^wim 

 and Lepidosteus a basal 

 element persists, bear- 

 ing several radials (Fig. 

 241) ; and here the fin 

 appears to be built on 

 the rhipidostychous 

 plan, with a post-axial 



axis Verv intprpqtino* Ventral view of the endoskeleton of the pelvic girdle 



axis. ^ ery mLer< .ing and fin of Pofyodon /oKum, Lac. (After Rautenfeld.) Pm, 



and important IS the median, and Pd, dorsal process of girdle ; F, F,, and F 2 , 



i i i. r ^ ' j nerve-foramina; 1-13, radials. 



skeleton of the paired 



fins in the Chondrostei (Davidoff [98], Wiedersheim [492], 



Kautenfeld [343], Thacher [434], Salensky [380], Mollier [301]). 



FIG. 277. 



