CHARACTERS OF FISHES. 347 



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- 

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

 gether rudimentary. A radius and ulna (fig. 128, 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 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" (*>., 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 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- 

 metrically disposed in pairs. Most commonly, the median 

 fins consist of one or two expansions of the dorsal integument, 

 called the "dorsal fins" (fig. 129, d y d') ; one or two on the 

 ventral surface near the anus the " anal fins " (fig. 129, a) and 

 a broad fin at the extremity of the vertebral column, called the 



* 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. 



