100 

 EXPLANATION OF TERMS, &c. 



Tej^ms relating to the Head. 



Snout. — The upper part of head situate in front of eyes. 



Occiput. — The hinder part of the head or skulh 



Gill-cover. — Con.'^ists of four broad flat bones joined together 

 on each side of the head. The anterior -with vertical free 

 margin is called the prcF-opercidum ; the upper posterior 

 bone, the operculum ; the lower posterior bone, the sub- 

 operculum ; and the bone forming the base, the inter- 

 operculum. 



Gill-opening.— T\ie vertical opening or slit leading to respira- 

 tory organs, — the gills. 



Branchiostegals. — The bony rays supporting the membrane 

 or cover to the gill-opening. 



Maxillary. — The second bone of upper jaw, often flat and 

 inflated, and sometim.es armed with teeth. The inter- 

 maxillary or prcE-maxillary is the anterior bone of upper 

 jaw. 



Mandibles. — The bones of lower jaw. 



Vomer. — The thin bone over roof of mouth dividing nostrils, 

 the base sometimes armed with teeth. 



Palntines.— Bones situate on either side of vomer, the base 

 sometimes armed Mith teeth. 

 Terms relating to the Body. 



The body is composed of head and timnk. It is compressed 

 and elevated when it is flattened laterally, as in the Bas- 

 tard Dorey. It is depressed when flattened vertically, as 

 in the Skate. It is elongate when shaped like the Salmon. 

 The narrow extremity of tail is termed the j^^duncle. 



The Lateral line is the median line along the sides of certain 

 fishes formed by a series of pierced scales. The latter are 

 sometimes interrupted, and may be in one or more rows 

 longitudinally. 

 Terms relating to the Fins. 



Usually there are two '' paired '' fins on fishes, corresponding 

 to, or, as they are termed, the homologues of the fore and 

 hind limbs of the higher vertebrates. The first pair 

 (pectoral), when present are situate under the shoulder, 

 ; close to gill-opening. The second pair (ventral) are 



variously placed, — under the chin they Sire jugular ; under 

 pectoral, or shoulder, thoracic ; behind shoulder, abdominal. 

 The following are unpaired :— The dorsal ^n or fins are 

 situate on the median line of the back ; the anal on the 

 median line between vent and caudal fin ; the caudal is 

 placed vertically on the extremity of vertebrae or tail. 

 When the latter is deeply notched, it is Jorked or furcate ; 

 when margin is concave, emarginate ; convex, rounded; 

 straight, truncate. 



Finlets. — Small detached rudimentary fins situate behind 

 the dorsal and anal fins, as in the Barracouta. 

 Terms relating to the Fin Rays. 



The fins are either rayless. when composed of a simple fatty 

 integument or skin (adipose), or the membrane is sup- 

 ported by fine or stout rays, composed of bone or cartilage. 



