PISCES. 145 



may be as well to name the chief positions in 

 which they occur. In some members of the great 

 Salmon family, for instance, we find a row of 

 teeth on the bone that forms the middle ridge of 

 the palate, which is called the vomer ; on each side 

 of this is another row on the palatine bones ; 

 and outside these is another pair of rows on the 

 upper jaw-hones. In the lower half of the mouth 

 the tongue carries a row of teeth along each edge, 

 which, when the mouth is closed, lock in between 

 the vomerine and the palatine teeth ; wliile the 

 loiver jaw-hones are also armed, each with a row 

 which locks in between the ptalatine and the upper 

 jaw {inaxillary) teeth. In other families we find 

 teeth on the bony arches of the gills^ on the bones 

 of the throat {p)harynx)^ or on the bones called the 

 inter-maxillaries, that lie partly before and partly 

 between the upper jaws. 



Fishes have cold blood ; that is to say, the blood 

 does not, in general, rise appreciably above the 

 temperature of the element in which they swim. 

 It is invariably red. The heart consists of one 

 auricle and one ventricle, wliich receive the blood 

 from the veins, and send it to the gills for re- 

 newal by the absorption of oxygen ; whence it is 

 circulated through the body in arteries. Both 

 the arteries and the veins are perfectly closed 

 vessels. 



The breathing-organs {gills) consist ordinarily 

 of many rows of thin membranous plates hung on 

 slender arches of bone. These organs are placed 

 on each side of the head, and are usually protected 

 by a great bony plate (the gill-cover) , made up of 

 several pieces. The water to be breathed is taken 

 in at the mouth, passes over the gill-membranes, 



L 



