CHARACTERS OF FISHES. 369 



is. often another bone, sqmetimes single, but oftener of two 

 pieces, attached to the upper end of the coracoid, and this is 

 believed to represent the collar-bone or clavicle.* 



The fore-limb possesses in a modified form most of the 

 bones which are present in the higher Vertebrata, The hum- 

 erus, or bone of the upper arm, is usually wanting, or it is alto- 

 gether rudimentary. A radius and ulna (fig. 136, r, u) are 

 usually present, and are followed by a variable number of 

 bones, which represent the carpus, and some of which some- 

 times articulate directly with the coracoid. The carpus is fol- 

 lowed by the " rays " of the fin proper, these representing the 

 metacarpal bones and phalanges. The pectoral fins vary much 

 in size and in other characters. In the Flying Gurnard (Dae- 

 tylopterus), and the true Flying Fish {Exoccetus), the pectorals 

 are enormously developed, and enable the fish to take exten- 

 sive leaps out of the water. 



The hind-limbs or " ventral fins " are wanting in many fishes, 

 and they are less developed and less fixed in position than are 

 the pectoral fins. In the ventral fins no representatives of the 

 tarsus, tibia and fibula, or femur, are ever developed. The 

 rays of the ventral fins — representing the metatarsus and the 

 phalanges of the toes — -unite directly with a pelvic arch, which 

 is composed of two sub-triangular bones, united in the middle 

 line and believed to represent the ischia. The imperfect pelvic 

 arch, thus constituted, is never united to the vertebral column 

 in any fish. In those fishes in which the ventral fins are 

 "abdominal" in position {i.e., placed near the hinder end of 

 the body) the pelvic arch is suspended freely amongst the 

 muscles. In those in which the ventral fins are " thoracic " or 

 "jugular" (i.e., placed beneath the pectoral fins, or on the 

 sides of the neck), the pelvic arch is attached to the coracoid 

 bones of the scapular arch, and is therefore wholly removed 

 from its proper vei tebra. 



In addition to the pectoral and ventral fins — the homologues 

 of the limbs — which may be wanting, fishes are furnished 

 with certain other expansions of the integument, which are 

 " median " in position, and must on no account be confounded 

 with the true " paired " fins. These median fins are variable 

 in number, and in some cases there is but a single fringe 

 running round the posterior extremity of the body. In all 

 cases, however, the median fins are " azygous " — that is to say, 

 they occupy the middle line: of the body, and are not sym- 



• These are the views entertahied by Owen as to the composition and 

 nature of the pectoial arch of fishes, but they are dissented from by Mr 

 Parker, one of the greatest living autliorities on this subject. 



