PECTORAL FINS OF POLYPTERUS. 



299 



I can find no explanation of the small cartilage attached to the 

 extei^nal side of the propterygium abont two-thirds of the length 

 from its base. It is not shown in Bndgett's larval form, but in a 

 Polypterus 13 cm. long I found it similar to that in the adult. 

 In one specimen, 18 cm. long, thei^e was an ossified outgrowth 

 terminating in a cartilaginous epiphysis at this place (text- 

 fig. 59). 



The small distal cartilages have many variations. Usually 

 they alternate with the radials and do not appear to be their 

 terminal segments, as was thought by Gegenbaur when he tried 

 to establish the homology of the radials and the propter-ygium 



Text-fig. 60. 



Fin of Folypterui with proximal fusion of propterygium and metapterygium. 



and metapterygium ; but when a multiplication of the carti- 

 laginous segments occurs, as frequently happens, these additional 

 ones are terminal (text-fig. 58, A, B). 



In a specimen 35 cm. long the propterygial and metapterygial 

 proximal epiphyses of the left fin were completely united ; the 

 propterygium and metapterygium were also completely fused for 

 a distance of 5 mm. This is an interesting variation in support 

 of Klaatsch's theory that the pentadactyle limb is derived from 

 the Polypterus type of fin, the humerus being formed from a 



20* 



