i6S 



OUTLINES OF ICHTHYOLOGY. 



Perch both these bones and tlie pterygoid 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 relative positions of the bones composing 

 the gill-covers, or opcrctila, will perhaps be more 

 easily distinguished by a reference to the accom- 

 panying diagram of the head of a Trout, in which — 



A represents the prc-opcrcuhnn, or fore-gill cover. 

 B, the operculum, or gill-cover proper. 

 c, the sub-opercuiuni, or under gill-cover. 



D, the inter-operculum, or intermediate gill-cover. 



E, the branchiostt'gous rays, or gill rays.' 



It will thus be seen that the gill-covers consist 

 of four pieces each : — t\\<t pi^c-opa'C7ilum, or foregill- 

 cover, A ; the opcrcuhun, or gill-cover proper, b ; 



From the Greek hninchia, gills, and sicgcin, to cover. 



