FISHES. 315 



a few genera, the poslerlor dorsal fin is destitute of rays, 

 and has obtained the name of pinna adiposa or flesh-fin. 



As these rays serve to support the fins, and are capable 

 of approaching or separating like the sticks of a fan, we 

 may conclude that they move upon some more solid body 

 as a fulcrum. Accordingly, we find in the sharks, for ex- 

 ample, that the rays of the pectoral fins ai-e connected by a 

 cartilage to the spine. In the osseous fishes, the pectoral 

 fins are attached to an osseous girdle which surrounds the 

 body behind the branchiae, and which supports the poste- 

 rior edge of their aperture. This osseous girdle is formed 

 of one bone from each side, articulated at the posterior su- 

 perior angle of the cranium, and descending under the neck, 

 where it unites with the corresponding bone. Between the 

 rays of the fin and this bone, which resembles the scapula, 

 there is a range of small flat bones, separated by cartilagi- 

 nous intervals, which may be compared to the bones of the 

 carpus. The rays of the ventral fins are articulated to 

 bones which correspond to the pelvis in the higher classes 

 of animals. The pelvis is never articulated with the spine, 

 nor does it ever form an osseous girdle round the abdomen. 

 In the jugular and thoracic fishes, it is articulated to the 

 base of the osseous girdle which supports the pectoral fins. 

 In the abdominal fishes, the bones of the pelvis are never 

 articulated to the osseous girdle, and are seldom connected 

 with each other. They are preserved in their situation by 

 means of certain hgaments- The rays oi the caudal fin are 

 articulated with the last of the caudal vertebrae, which is, 

 in general, of a triangular form, and flat. The rays of the 

 dorsal fin are supported by little bones, which have the 

 same direction as the spinous processes, and to which they 

 are attached by ligaments. 



As connected with the fins, we may here notice those 

 organs which are termed cirri or tcniacida, according as 



