1'AIHED KINS. 



25 



very slight fusion in the pectoral (fig. 21 A). It is very im- 

 portant to notice, however, that in both these fins, there are 

 between the distal ends of the unaltered parallel bars the 

 remnants of similar bars which have evidently been reduced 

 and displaced by growth-pressure, just as the middle digit 

 sometimes becomes reduced and displaced from connection 



Fio. 23. 



Eusthenopteron foordi ; pectoral fin, nat. size. U. Devonian ; Scaumenac Bay, 

 Canada, b, basal cartilage ; I, II, III, three separate branches ; x, base 

 apparently of a fourth branch ; 1, 2, 3, three successive segments ; the 

 greater part of the fin formed by the articulated and subdivided dermal 

 rays. Right border preaxial, left border postaxial. (From specimen in 

 British Museum, no. P. 6796.) 



with the carpus in Ichthyosaurus, some marine mammals, and 

 birds. The next important paired fin of which we know the 

 supports, is the pectoral of Pleuracanthus (fig. 22), of Car- 

 boniferous and Permian age. Here the arrangement is the 



