OUTLINES OF ICHTHYOLOGY. 171 



of the spiny-firmed species are enabled to progress 

 upon dry land, and even to travel considerable 

 distances from one pool to another. The pec- 

 torals are supported by two bones behind the 

 gills, one on each side, which are sometimes im- 

 bedded in the muscles, and sometimes connected 

 with the spine, but more generally attached to the 

 bones of the head. The ventrals are commonly 

 attached to the sides of the belly. 



The Teeth of fish are closely connected with 

 the fins and gills, as furnishing marks by which the 

 sub-genera may frequently be distinguished, and 

 are so permanent in their characters in each spe- 

 cies as to be well worthy of particular attention. 



In different families, however, teeth differ very 

 materially both in situation, number, and form, and 

 also even in different species of the same family. 

 An instance of this is seen in the dental arrange- 

 ment of the several species of Salmonidce, be- 

 tween which they furnish one of the readiest 

 and most reliable means of distinguishing. 



Again we find many families that are almost, 

 if not wholly, toothless ; whilst others possess 

 teeth on all the bones which assist in forming 

 the cavity of the mouth, and even on the bones 

 of the throat, or pharynx, behind these. This 

 latter is particularly the case in the herbivorous 

 fishes. Sometimes the teeth are uniform in shape 

 on the various bones of a single mouth. In 



