122 LECTURE V. 



jointed ray splits easily into two lialves as far as its base, and ap- 

 pears 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 " Malacopterygians " and " Acan- 

 thopterygians :" 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 

 {Sihirtis). In the Gurnards 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 enlargements of the spinal chord, and they appear 

 to be organs of exploi'ation. In all the Grurnards the locomotive part 

 of the pectoral member is of large size ; but in one species {Dacty- 

 lopterus) 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 development in the true 

 Flying-fish {Exoccetus). 



Only in the Polypterus can any segment analogous to a metacarpus 

 be distinguished by modification of structure from the phalangeal 

 portion of the fin-rays : there are seventeen simple cylindrical meta- 

 carpal bones (^Jig. 41. 37), the middle ones being the longest : they 



are supported on two carpal bones {ib. 

 56), almost as remarkable for their 

 length as in the Lophins ; a third 

 shorter and broader carpal is wedged 

 ~"'&7' into the interspace of the two longer 



Bones ol pectoral fin of Polypter^is. ^^^^^ ^^^ ^^^^ ^^^^ directly join the 



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 

 Salamandroid Fish in the carpal portion projecting freely from the 

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

 the diverging appendage of the scapular arch is reduced to the 

 condition of a single jointed ray {Jig. 27. 67). From this ele- 

 mentary form, development may be traced in one direction, through 

 osseous and cartilaginous fishes, in the progressive manifestation 

 of irrelative repetition of parts, until the number of jointed rays 

 exceeds a hundred, as in the fishes thence called "Rays"; and 

 in another direction, through the didactyle and tridactyle Pe- 

 renni-branchiate Reptiles, to the perfection of the more normal 

 type of the anterior member in liigher Vertebrata ; in each 

 class diverging in special directions, more or less, from that 



