ANATOMY OF VERTEBRATES. 1G7 



soft and jointed ray splits easily into two halves as far as its base, 

 and appears to be essentially a conjoined pair. 



In the series of Osseous Fishes the rays of the pectoral and 

 ventral fins offer the same modifications as those of the median 

 fins, on which have been founded the division into ' Malacoptery- 

 ' gians ' and ' Acanthopterygians : ' in the former, the last or ulnar 

 fin-ray, is usually thicker than the rest ; in the latter it is always 

 a hard, unjointed spine : in some Fishes it forms a strong pointed 

 or serrated weapon (Silurus). In the Gurnards, fig. 82, the three 

 lowest rays are detached and free, like true fingers ; and are soft, 

 multi-articulated, and larger than the rest ; they are supplied by 

 special nerves, which come from the peculiar ganglionic enlarge- 

 ments of the spinal chord, and are organs of exploration and of 

 subaqueous reptation. 1 In all the Gurnards the natatory part of 

 the pectoral member is of large size ; but in one species (Dactylo- 

 pterus) it presents an unusual expanse, and is able by its stroke to 

 raise and sustain for a brief period the body of the fish in the air. 

 The pectoral fins present a still greater developement in the true 

 Flying-fish (Exoccetus). 



In some Malacopteri and Ganoidei a segment analogous to a 

 metacarpus may be distinguished by modification of structure 

 from the phalangeal portion of the fin rays : in the Polypterus 

 there are seventeen simple cylindrical metacarpal bones, fig. 103, 

 57, the middle ones being the longest : they sustain thirty-five 

 digital rays, and are supported by 103 



carpal bones, ib. 103, 56, of which 

 two are almost as remarkable for 

 their length as in the Lophius ; the 

 third, shorter and broader, is wedged 

 into the interspace of the two longer "*%?' 



ones, but does not directly join the Bones 0l pectoral fln of r ° l 

 metacarpus. The carpus is supported by a small radius, 55, and 

 ulna, 54, which articulate directly with the coracoid. A further 

 approach to the higher conditions of the pectoral member is made 

 by the same Fish in the carpal portion projecting freely from the 

 side of the body, as in the Lophioid Fishes. In the Salmon, 

 where eleven such metacarpals support thirteen or fourteen fin- 

 rays, the carpus is short and consists of four bones. 



In the Plagiostomes the scapular arch is detached from the oc- 

 ciput, the conditions of its displacement being the more varied and 

 vigorous use, or the enormous expanse, of the pectoral fin ; per- 



1 CLix. p. 46. 



