624 



SCAXUINAVIAN FISHES. 



l);iTt ()t" each ray in the dorsal tin. The fle.\(n"s of the 

 anal tin, also divided into a surface-layer and an under- 

 layer, originate from the bodies of the iiindinost ab- 

 dominal vertebra', fi-om tlie caudal vertebra- witii tlieir 

 inferior processes and interhajmal bones, and from the 

 under surface of the horizontal fibrous membrane, and 

 are attached to the raj's of the anal tin in the same 

 manner as we have just describ(!d in the case of the 

 flexors of the dorsal tin. The flexors of the caudal fin 



Kf mpd 



Fig. 15G. Position of the iiniscles iiiid viscera in Orthaijoiiscus ruola, 

 on a reduced scale. After Clelanu. 

 mpu, the flexors of the anal fin (musciili piiinw ciiiaiis); sf, the 

 librous dividing membrane {septum Jibrosum); mpd, the flexors of the 

 dorsal fin {musculi pinncc dorsalis) ; maa, the anterior abdominal muscle 

 (m. abdomuudis anterior); h, the liver; I, the ligament between the 

 intestinal sac and the liver; i, the peritoneal investment of the in- 

 testines (intestinal sac); p, the peritoneum, opened and partly removed; 

 map, the posterior abdominal muscle (m. abd. posterior); a, the vent; 

 mpc, the flexors of the caudal fin (m. pinnce caudalis). 



(mpc) form no compact muscular mass; each of the rays 

 in the caudal tin is furnished on each side with a spe- 

 cial, ventricose muscle, and these muscles start partly 

 from the bodies of the hindmost vertebra^, partly from 

 the supporting bones of the caudal tin (the hindmost 

 interneural and interhtemal bones), partly from the 

 superior and inferior folds of the liorizontal, inter- 



muscular, tibrous membrane (sf). (.)f the system of the 

 large lateral muscles there remain only two abdominal 

 muscles, belonging to the under-layer of the system, 

 the first (map) starting from the top of the clavicle, the 

 second {maa) from the coracoid bone, and both attached 

 to the outer surface of the strong peritoneum {p). So 

 great is the UKjdification both of the skeleton and of 

 the musculature that has accompanied the late develop- 

 ment of the caudal fin, and rendered the dorsal and anal 

 tins the principal organs of locomotion. These two tins 

 have attached to themselves, from the very beginning, 

 the great mass of muscles and supjiorting bones; while 

 the caudal fin has become a secondary organ, ^vhich has 

 been forced to adapt its development to pre-exist ent 

 circumstances, and which has thus sunk almost to an 

 adipose fin, though thin osseous rods have been deve- 

 loped to rays within it. The influences of this revolu- 

 tion in the development of the oi'gans of motion have 

 also affected the central nervous system. The family 

 is remarkable, from an anatomical point of view, not 

 only for the insignificant size of the brain", which is 

 extraordinarily small, even within tlie class of fishes, 

 but also for the fact that the spinal marrow, soon after 

 its passage through the occipital foramen, ramifies in 

 the well-known '"horsetail form" {cnnda eijtthia), without 

 being continued any further in tlie form of a continuous 

 chord within the spinal canal''. 



Whether more than two species may be distinguished 

 with certainty witliin this family, must still be regarded 

 as a doubtful (luestion. Ranzaxi's attempt' to establish 

 16 species, distributed among 6 genera, has long ago 

 been abandoned as futile; and Putnam's evidence in 

 favour of the opinion that the young specimens described 

 by KoLREUTEK, Pallas, and others belong to a distinct 

 species of a separate genus'', seems to require fui'ther 

 confirmation. It has also been proposed' to i-efer the 

 two established species to two distinct genera, one of 

 which, Banzama, with more elongated body and with 

 the dermal covering smooth but divided into hexagonal 

 plates, has been met with on the English coast, but 

 never, up to the present time, within the limits of the 

 Scandinavian fauna. 



" In large specimens of Ortbai/oriscns mola, according to HARTiNr., the brain may weigli no more than ' 'jis'mh '• ^- '^"t quite 0'000014, 

 of the total weight of the body. 



' Arsaky, De piscium cerebro et medulla spinali, Halle 1813, p. 4, tali. Ill, fig. 10. 



' Nov. Comm. Acad. Scient. Inst. Bonon. Ill (1839). 



■' Proc. Amer. Assoc. Adv. Sc, 19th Meeting (1870), p. 255. 



' Steenstrup and LtJTKBN, Overs. Vid. Selsk. Forh. Kbhvn 18G3, p. 42. 



