528 



THE OCEAN WORLD. 



consisting generally of a fold of the skin, supported by slender, 



flexible, cartilaginous or osseous rays, connected by a thin membrane. 



The muscles which bind together the vertebral column are so 



much developed in fishes, as well as others of the superior animals, 



>, "'.' 



s/' 



Fig. 348. — Skeleton of the Common Perch. 

 a. the inter-maxillary bone ; b, the ma.\illary bone ; c, the imder jaw ; d. the palatine arch ; 

 e, cranium ; /, the inter-operculum ; ^ g^, the vertebral column ; k, the pectoral fin ; 2, the ventral 

 fin ; k and /, the dorsal fins ; w, the anal fin ; «, the caudal fin. 



that they constitute in them alone the principal part of the body. The 

 caudal, dorsal, and anal fins act as outlying oars ; the pectoral and 

 ventral fins assist in progression, at the same time that they help to 



Fig. 349. — Swimming bladder of the Carp. 



maintain the equilibrium of tlie fish and guide and direct its move- 

 ments, which are generally astonishing from their rapidity. 



An organ, which is only met with in fishes, though not to be 

 found in all species (Fig. 349), and which is usually considered as 

 their chief aid in floating, is a large bladder situated within the 

 body, between the dorsal spine and the abdomen ; this is usually 

 called the swimming bladder. According to the volume this bladder 



