CHARACTERS OF FISHES. 393 



Lastly, there is often another bone, sometimes single, but 

 oftener of two pieces, attached to the upper end of the cora- 

 coid, 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 

 humerus, or bone of the upper arm, is usually wanting, or it is 

 altogether rudimentary. A radius and ulna (fig. 165, 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 (Dac- 

 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 wan ting 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 vertebra. 



In addition to the pectoral and ventraHins 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, 



* These are the views entertained by Owen as to the composition and 

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

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



