OUTLINES OF ICHTHYOLOGY. 167 



column varies greatly from sixteen, for instance, 

 in the Sunfish (and fewer in other species) to 162 

 in the Conger Eel, and upwards of 230 in the 

 Electric Eel. The shapes of vertebrae also vary, 

 though commonly their centra, or bodies, are more 

 or less narrowed in the middle like an hour-glass. 

 The ends are cup-shaped, and the cups filled with 

 a bag of gelatine enclosed in a strong membrane, 

 which, being united round the rims, forms a very 

 elastic joint. 



The head in various species differs much in 

 form, but in general consists of the same number 

 of bones as in other vertebrate animals. Of these, 

 the most important to the naturalist are the bones 

 forming the gills, 1 and those constituting the jaws. 2 



Amongst the latter the inter- or pre-maxillary 

 forms in most fishes the edge of the front of the 

 upper jaw, having the maxillary behind it. The 

 situation of the palatine bones is in the roof of the 

 mouth, one on each side of the vomer ; and in the 



1 Opercula (from operculum^ Latin for a lid, or cover). 

 Sub-Operculum. 



Inter-Operculum. 

 Pre-Operculum. 



2 Transverse, or pterygoid. 



Palatal, or palatine bones (bones of palate). 



Vomer (from vomtr, Latin for ploughshare). 



Nasal. 



Superior Maxillary, or maxillary (from maxilla, a jaw, Latin). 



Inter-maxillary, or pre-maxillary. 



Articular portion, &c. 



Dental portion of the lower jaw, or inferior maxillary bone. 



