174 COMPARISONS OF STRUCTURE IN ANIMALS. 



vertebral column cannot be bent at an abrupt 

 angle, and whoever will watch the actions of a 

 fish in the water -will see, that Avhatever degree 

 of flexure the caudal portion may display, the 

 curve is regular and graceful. 



It is only laterally in such fishes as the 

 perch, carp, salmon, and others, that the flex- 

 ure of the spine occurs ; the muscles being so 

 arranged as to act accordingly. Yet it may be 

 observed, that the processes of the vertebrte, 

 the bodies and union of which we have de- 

 scribed, forbid flexure in any other direction ; 

 thus the vertebrae, and the muscles that govern 

 them, are in just harmony. Each vertebra 

 gives off a large upper spinous process, arising 

 firom a double origin, so as to form an arch at 

 its base. The multiplication of these arches 

 forms a canal for the lodgment of the spinal 

 cord, which is thus protected as it runs along 

 the spine. Similai' processes, called the infe- 

 rior spinous processes, proceed from the under 

 part of the bodies of the caudal vertebrae, and 

 through the canal at their base the aorta is 

 transmitted in its passage along the spine. 



The number of the vertebraj varies consider- 

 ably in difi'erent fishes. In some we count 

 only from thirty to forty ; but the spine of the 



