INTRODUCTION. 83 



caudal; and have each the same kind of upper 

 spinous process, often with its appendages, the 

 interspinous bone, and the ray, of the fin still 

 called dorsal, as the abdominal vertebrae. Instead, 

 however, of the two transverse processes, and their 

 appendages the abdominal ribs, which characterize 

 the abdominal vertebras, the caudal vertebras have 

 a second spinous process, with two roots, pointing 

 obliquely downwards from the body of the vertebrae ; 

 and, connected with this lower spinous process, 

 exactly in the same manner as the corresponding 

 parts are with the upper one, a second interspinous 

 bone, and a ray of the anal jin^ lying near the tail 

 of the animal, and on the opposite surface of the 

 body from the dorsal. The caudal Jln^ lastly, or 

 what is commonly called the tail of fishes, is an 

 appendage, like a portion of the dorsal, and the 

 whole of the anal fin, to the caudal vertebrae ; to 

 the upper and lower spinous processes of which it 

 is attached, almost directly in the axis of the 

 spine, forming, in appearance, a kind of fan, moved 

 by powerful flat muscles. It will hence be obvious, 

 that the dorsal fin, the anal fin, and the caudal fin, 

 are, in fact, only appendages to the spinal column 

 of fishes; the two former being, in reality, de- 

 velopements of the spinous processes. These are 

 used chiefly directing ; and, from their position, 

 except in giving greater power to the rapid motion 

 of the body from side to side, are not directly 

 employed in progression or turning. 



Where the bodies of the individual vertebrae of 



