252 LECTURE X. 



In the Plagiostomes with the longitudinal spiral valve the main 

 I'oot of the portal vein is concealed in the free, thickened, muscular 

 margin of that valve * : the trunk of the intestinal vein is lodged 

 also in an internal fold of the mucous coat in the Lamprey : in the 

 Plagiostomes and Ganoids with transverse coils of the spiral valve, 

 the venous blood is collected into an external intestinal vein. In 

 the Paddle-fish this vein joins the vein of the spleen (^fig. 61. w), and 

 then, with the duodenal, pancreatic, and gastric veins, forms tlie por- 

 tal trunk. 



Professors Eschricht and MuUer f found, in the Tunny, that the veins 

 of the stomach, intestine, pyloric appendages, and spleen, respectively 

 subdivided into numerous minute venules, which interlaced with cor- 

 resj)onding ' retia mirabilia ' of the arterial branches sent from the 

 caeliac axis to the same viscera, and formed pyriform masses of 

 vessels before entering the liver. 



In a few Osseous Fishes, as the Shad, some of the caudal 

 branches of the vertebral system of veins anastomose with the 

 veins of the rectum, and tlius form part of the roots of the portal sys- 

 tem. But the most interesting modification of the portal system of 

 Fishes is that discovered by Retzius in the Glutinous Hag. In 

 this and also in other Myxinoids, the genital and intestinal veins 

 form a common trunk along the line of attachment of the me- 

 sentery : all the gastric veins that do not empty themselves into 

 the cardinal vein also join the great mesenteric vein. This vein 

 advances to the space between the pericardium and the right supra- 

 renal body, receives the anterior vein of that body (its posterior one 

 joining the cardinal vein), and dilates into an elongated sinus, which 

 is said to contract, as if it were a portal heart. The anterior part of 

 this sinus receives a vein from the right anterior parietes of the body, 

 which is formed by the union of all those veins of the muscular parts 

 there which do not join the right jugular vein : the portal arterial vein 

 is sent off from the posterior end of the pulsating sac, near the entry 

 of the mesenteric vein, and goes backwards to beneath the two livers, 

 and there divides, enters, and ramifies in each. The hepatic vein of 

 the hinder and larger liver enters the common trunk or sinus formed by 

 the union of the two cardinal veins with the left j ugular : the hepatic 

 vein of the smaller liver joins the termination of the left jugular vein, 

 and they together end in the opposite side of the same common sinus. 



In the Plagiostomes the right jugular and cardinal veins unite, and, 

 receiving the vein of the pectoral fin (brachial vein), and a superficial 

 vein from the head (external jugular), form a short transverse 



* Duvernoy, xcvi. p. 274. -j- ci. 



