GENERAL OUTLINES OF ICHTHYOLOGY. 29 



The head in various species differs much in form, but in 

 general consists of the same number of bones as in other 

 vertebrate animals, viz. a frontal of six pieces, parietal s of 

 three, occipitals of five, sphenoid of five, and two of each 

 temporal bone. 



Of these the most important to the naturalist are the 

 bones forming the gills, e, /, and g and those constituting 

 the jaws, r, s, t, v, w, x, y. 



Amongst the latter the inter- or pre-maxillary* (w} forms 

 in most fishes the edge of the front of the upper jaw, 

 having the maxillary (v) behind it. The situation of the 

 palatine f bones (s) is in the roof of the mouth, one on each 

 side of the vomer% (t) ; and in the Perch both these bones 

 and the pterygoid (r) carry teeth. The lower jaw, except 

 in the cartilaginous fishes, has generally two bones in each 

 side : a further reference to these bones will be found 

 under the division " Teeth." The bones to which the fins 

 are attached will be more conveniently noticed in the re- 

 marks on the latter organs. 



The relative positions of the bones composing the gill- 

 covers, or opercula , will perhaps be more easily distin- 

 guished by a reference to the accompanying diagram of the 

 head of a Trout, in which 



* So named from the Latin maxilla, a jaw. 

 t Palatine bones, or bones forming the palate. 

 Tomer, so called from a fancied resemblance to a ploughshare, for 

 which the name given is the Latin. 



Opercula, from the Latin operculum, a lid or cover. 



