528 THE OCEAN WORLD. 
consisting generally of a fold of the skin, supported by slender, 
flexible, cartilaginous or osseous rays, connected bya thin membrane. 
The muscles which bind together the vertebral column are so 
much developed in fishes, as well as others of the superior animals, 
a ‘ MEE 
5 We AA de COREE, Ll 
AER NS 
_ _ Fig. 348.—Skeleton of the Common Perch. 
a, the inter-maxillary bone ; 4, the maxillary bone; c, the under jaw ; @, the palatine arch ; 
e, cranium ; /, the inter-operculum ; gg, the vertebral column ; 4, the pectoral fin; z, the ventral 
fin; & and Z, the dorsal fins ; 7, 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 the 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 sazmming bladder. According to the volume this bladder 
