VASCCLAE SYSTEM OF FISHES. 251 



case enters the left or common cardinal vein.* In the Tunny the 

 two ' vense jugulares' unite and form a common trunk, "which 

 enters the auricular sinus independently. I The Shad, the Pike, 

 and the Lucioperca are examples where the jugular reins are 

 symmetrical, and terminate distinctly in the precaval veins. "With 

 regard to the vertebro -venal system of the trunk, not all the 

 segmental branches terminate in the ' vena cardinalis ; ' the 'neural' 

 or superior twigs form with the ' myelonal' veins a trunk wliich 

 runs parallel with the cardinal veins, but above the vertebral 

 bodies in the neural canal. This trunk, which I call the ' vena 

 neuralis,' communicates by short lateral and vertical canals with the 

 ' venfe cardinales, and in the region of the abdomen these short 

 anastomosing veins perforate the substance of the kidneys, and 

 receive the 'renal veins' before terminating in the abdominal car- 

 dinal veins. The 'neural vein' gradually exhausts itself by these 

 descending branches, and does not extend to or terminate anteriorly 

 in the precaval trunk. Jacobson, observing that the abdominal anas- 

 tomotic branches of the neural vein, in transferring its contents to 

 the cardinal veins, perforated the kidneys, thought that those branches 

 ramified in the renal tissue, like the portal veins in the liver ; but 

 my observations concur with those of Meckel and Cuvieri in 

 showing that they rather receive or communicate with the renal 

 veins i?i transitu in Osseous Fishes. In the Lamprey the renal vein 

 assumes the form of a cellular or cavernous sinus, of a very dark 

 colour, extending along the mesial margin of the kidney, uniting 

 with its fellow posteriorly, and communicating by small orifices with 

 the contiguous cardinal vein. 



The visceral system of veins commences in Osseous Fishes by the 

 capillaries of the stomach and intestines, of the pancreatic ca?ca and 

 spleen, of the generative organs and air-bladder : these, by progres- 

 sive union and reunion, constitute either a single trunk which forms 

 the portal arterial vein of the liver ; or, as in the Perch, a second 

 trunk, the true homologue of the ' inferior vena cava ' which returns 

 the blood from the genital organs and air-bladder to the auricular 

 sinus, without previous ramification in the liver ; the portal trunk 

 being formed only by the veins of the alimentary canal and its appen- 

 dages. The portal trunk is single in the Ling, the Burbot, the Pope, 

 the Eel, the Lamprey, and the Plagiostomes : but, in the Carp, where 

 the lobes of the liver interlace with the convolutions of the intestine, 

 the veins of this canal jiass directly into the liver by several small 

 branches, which ramify therein without forming a portal trunk. 



* XXI. ib. p. 38. t lb. p. 37. | xxiii. p. SSI. 



