3o: 



ACTINOPTER YG1I 



Fig. 276. 



Division 4. 



ACTINOPTER YGII. 



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 

 77 entirely supported by 



the dermotrichia. The 

 same is the case in the 

 median fins. It cannot 

 be said that there is anj' 

 evidence of a biserial 

 arrangement of the 

 radials in the paired fins 

 of the Actinopterygii, 

 yet it is usually sup- 

 posed that they have 

 been derived from such 

 , . an archipterygium by 



Ventral view of the cartilaginous skeleton of the pelvic . . <■ i -i 



girdle and fin of Scaphirhynchus. (After Rautenfeld.) the lOSS Of the post-axil 

 Pm, median, and I'll, dorsal process of girdle; F, nerve- __j;_ i_ /fX «.«.,.-« 1™.,- M kq 



foramen ; i-9, .adiais. radials (Uegenbaur [158, 



162], Braus [48]; see 

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

 fin of the Holostei, p 



where the few remain- F 



ing radials articulate 

 directly Avith the pelvic 

 bone (Figs. 245 - 8). 

 This is also the case 

 with the pectoral fin 

 of the Teleostei (Figs. 

 243,480). Bnt in Jmia 

 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. Very interesting 

 and important is the 

 skeleton of the paired 

 fins in the Chondrostei (David off [98], Wiedersheim [492], 

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



Fig. -277. 



Ventral view of the endoskeleton of the pelvic girdle 

 and fin of Polyodon folium, Lac. (After Rautenfeld.) Pm, 

 median, and I'd, dorsal process of girdle; F, F\, and Fo. 

 nerve-foramina ; 1-13, radials. 



