464 



ANATOMY OF VERTEBRATES. 



Dr. Joseph Jones l has pushed this kind of analysis further, as 

 shown by the subjoined table. 



82. Veins of Fishes. As the blood moves in a circle, it 

 signifies little at what point we commence the description of the 

 parts in which it flows. But as, in tracing the progress of the 

 nutriment through the organs concerned in its chylification and 

 sanguification, we were led by the lymphatics to the veins, we 

 begin with them the account of the circulating system in the 

 present class. 



The tunics of the veins of Fishes are unusually thin, and their 

 valves few : though commonly in the form of tubes, yet they more 

 frequently dilate into sinuses than in the higher classes, and traces 

 of the diffused condition of the venous receptacles, so common in 

 the Invertebrates, are not wanting in Fishes ; as, for example, in 

 the fissures of the renal organs, where the veins seem to lose their 

 proper tunics, or to blend them with the common cellular tissue 

 of the part ; and in the great cavernous sinus beneath the abdo- 

 minal aorta, receiving the renal and genital veins in the Lamprey. 

 The jugular veins of Osseous Fishes and the hepatic veins of the 

 Rays form remarkable sinuses. The very delicate fibres of the 

 proper venous tunic affect a longitudinal disposition : and in many 

 of the veins of Fishes the walls show pigment, usually in the form 

 of stellate cells. 



The veins of Fishes constitute two well-defined systems ; viz. 

 the f vertebral ' and the ' visceral,' answering to the division of the 

 nerves and muscles into those of f animal ' and ( organic ' life : the 



o 



portal system is a subdivison of the visceral one, but also fre- 

 quently includes part of the vertebral system of veins, especially 

 in the Myxines, in which the portal sinus forms a common meeting- 

 point between portions of both systems. 2 



The capillary system of vessels consists in Fishes, as in other 

 Vertebrates, of minute but similar-sized tubules, capable of carrying 



1 CCXLV. p. 27. 



2 Retzius, iu xxi. * Gefiisssystem,' 1841, p. 16. 



