LOCOMOTION OF FISHES. 103 



which, in most fishes, is quite rudimentary ; so 

 much SO, that the two bones of the fore-arm seem 

 to be in general almost directly connected with the 

 scapula, no proper bone being interposed between 

 them. The shoulder-joint, therefore, and the 

 elbow-joint of fishes, are, in general, almost one 

 and the same. The two bones of the fore-arm are 

 the ulna and the radius ; which two bones are, in 

 some few fishes, so constructed, as to roll with 

 tolerable fi'eedom on each other, exactly in the 

 same way as they roll on each other in man, in the 

 action of rotating the hand: and it is by this 

 means that they have the power of changing the 

 direction of the flat part of their pectoral fin, during 

 its play in the water ; a power which, ias we shall 

 presently find, is so conducive to the full use of 

 this organ. These two bones, however, are firmly 

 united together in most reptiles, in aU birds, and in 

 many quadrupeds ; so that here, again, certain 

 fishes have the advantage of many of the superior 

 tribes of animals. To the ulna and radius are- 

 attached the several bones of the wrist, quite cor- 

 responding to those of the wrist of man ; and from 

 these, again, proceed the long radiating bones, 

 equally corresponding to those of the hands and 

 fingers of man, and constituting, with the mem- 

 brane extending between them, all that is seen, on 

 a superficial view, of a pectoral fin, and all in 

 which such a fin is vulgarly supposed to consist. 

 It is not peculiar to fishes, however, to have a 

 great pai*t of these anterior extremities concealed 



