268 THE FRESH- WATER FISHES OF EUROPE. 



The lower jaw is elevated in the middle, so as to form a blunt projection in 

 front. The teeth are directed backward (Fig. 146). The head of the vomer is 

 pentagonal and toothless. The stalk of the bone usually has three or four teeth 

 in a single row. In old fish they are gradually lost from behind forward. 

 There are three or four teeth on each side of the tongue ; they are as strong 

 as those in the maxillary bone ; the sixteen or seventeen teeth in each pala- 

 tine bone are weaker, and the row is but little curved. The opercular plates 



are rounded at their edges. The 

 pre-operculum has a distinct lower 

 limb. There are eleven branchio- 

 stegal rays on each side ; the large 

 pseudobranchiae are comb-shaped. 



The dorsal fin begins in front of 

 the middle of the body ; it is at 

 least twice the length of the head 



high, and truncated behind so that 

 the last ray is two-fifths of the length of the third and fourth rays. The 

 adipose fin is opposite to the end of the anal, and twice as high as long. 

 The last ray of the anal fin is only one-third of the length of the longest ray. 

 The pectoral fin is comparatively small and scarcely one-tenth of the length 

 of the fish. The caudal fin is deeply cleft in young individuals, which 

 have the longest rays of the fin more than twice the length of the middle rays. 

 The forked or emarginate condition may remain till the fish is more than two 

 feet long, when the fin becomes more or less truncated. 



The hinder part of the body is elongated, and covered with relatively large 

 scales, there being constantly eleven or sometimes twelve in a transverse series 

 running from behind the adipose fin obliquely forward to the lateral line. The 

 scales are rather small ; they are ovate and marked with wavy fine concentric 

 lines. Giinther counts 120 in the lateral line; Day 120 to 125, and Heckel 

 and Kner 130; and the number of scales seems to vary between these limits 

 in the Salmon of North Germany. The course of the lateral line is horizontal 

 and rather above the middle of the height of the body. The cephalic canals 

 open on the head, with distinct rows of pores. There are eight or nine pores 

 on the sub-orbital branch, and five or six pores on the mandibular branch. 

 The number of vertebrae is fifty-nine or sixty. The pyloric appendages, which 

 are at first very slender, vary in number from fifty-three to seventy-seven, and 

 as the fish comes up from the sea these organs are invested with fat, so that 

 fully five ounces of fat were removed from them by Buckland in large Rhine 

 Salmon. 



