144 PISCES. 



present an extensive external one. The body is in 

 general covered with scales, which are pieces of 

 bone developed from the skin, and overlapping 

 each other. But more essential to the Fish are 

 certain series of sword-like bones, which penetrate 

 the flesh along the line of the back, along the line 

 of the belly, and around the extremity of the spine, 

 to which are jointed bony or flexible rays, re- 

 sembling those of the true limbs, and, like them, 

 united by membrane. These series are important 

 instruments of locomotion, and are designated 

 respectively, the back-fin (dorsal), the vent-fin 

 (anal) , and the tail-fin (caudal). 



The teeth of Fishes vary exceedingly in form, 

 arrangement, and position. " The most common 

 shape is that of an elongated cone, either straight 

 or curved. When the conical teeth are small and 

 numerous, they are compared to the points of the 

 cards used for carding wool or cotton j and they 

 are sometimes so slender, yet so dense from their 

 numbers, as to resemble the pile of velvet or 

 plush ; and often, from their very minute size, their 

 presence is more readily ascertained by the finger 

 than by the eye. Some fishes have in the front 

 of the jaws flat teeth with a cutting edge, like a 

 true incisor ; others have them rounded or oval ; 

 they are then most frequently planted in rows, and 

 adapted to bruise or crush the various substances 

 with which they are brought in contact."* 



Unlike the MAMMALIA, in which the teeth are 

 confined to the jaws, Fishes may have every bone 

 that assists to form the cavity of the mouth and 

 throat furnished with these organs. As they con- 

 stitute important characters for identification, it 



* Yarrell's "British Fishes," i. 113. 



