8 BONES OP THE EXTREMITIES OF FISHES. 



ing at their summit ; these are termed articulated or soft rays ; 

 the caudal fin is entirely formed of them (Fig. 346) ; and some- 

 times there are no others. 



544. The lateral fins, which represent the members, are ter- 

 minated by rays similar to those of the vertical fins, and analo- 

 gous to the fingers. In the pectoral fin are seen, at the base of 

 these appendages, a transverse series of four or five small bones 

 (c a, Fig. 348), which arc analogous to those of the carpus ; and 

 these, in their turns, are fixed to two flat bones, a 5, which seem 

 to be the radius and ulna widened. This apparatus is supported 

 by a kind of bony girdle situated immediately behind the ears, 

 on which the operculum or gill-cover is fixed ; and it consists of 

 three bones, extending from the cranium to the hyoid apparatus, 

 and prolonged backwards into a pointed process. The principal 

 piece which enters into its composition, is that which bears the 

 fore-arm, and which may consequently be regarded as the hume- 

 rus, h ; it is united below with that of the opposite side and 

 with the central prolongation of the hyoid apparatus ; and it is 

 connected with the cranium by two bones (o, 0'), which are 

 regarded by Cuvier as analogous to the scapula ; and lastly, the 

 pointed process which is prolonged over the sides of the body, 

 is ordinarily formed of two pieces, and may be compared to the 

 coracoid bone, co. The posterior member is less complicated; 

 the rays of the ventral fin are only supported on a single bone, 

 usually of triangular form, which is frequently attached to the 

 central portion of the osseous girdle of the anterior member, and 

 which, in other instances, is merely suspended by the muscles, 

 having no bony connexion with the skeleton of the trunk. 



545. In Cartilaginous fishes, such as the Rays and the Sharks 

 (of which the Dog-fish is a common species), the arrangement 

 of the skeleton differs from that which we have already described, 

 and exhibits a great resemblance to that of the still cartilaginous 

 skeleton of the Tadpole. The skull is not divided by sutures, 

 and is only composed of a single piece ; this, however, is formed 

 in other respects very nearly like the skull of ordinary Fishes. 

 The upper jaw is formed by pieces analogous to the palatine 

 bones and the vomer ; the maxillary and the intermaxillary do 



