468 



ANATOMY OF VERTEBRATES. 



veins of the rectum, and thus form part of the roots of the portal 

 system. But the most interesting modification of the portal 

 system of Fishes is that discovered by Retzius in the Glutinous 

 1 1 ag. In this and also in other Myxinoids, the genital and intes- 

 tinal veins form a common trunk along the line of attachment of 

 the mesentery : 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 

 suprarenal 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 ante- 

 rior part of this sinus receives a vein from the right anterior 

 parietes of the body, which is formed by the union of all those 

 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 

 backward 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 jugular : the hepatic vein of the smaller 

 liver joins the termination of the left jugular vein, and they toge- 

 ther 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 ' precaval ' trunk. A corresponding precaval trunk is 

 formed in the same way on the left side, and the great auricular 

 sinus is constituted by these and by the wide hepatic veins, Avhich 

 contract before they terminate. In many Osseous Fishes, as 

 Salmo, Siluriis, Belone, Anguilla, Ammodytes, and Accipenser, 



the hepatic veins terminate in the 



common sinus by a single trunk ; 



in others, as Thynnus, Gadus, 



JEsox, and Pleuronectes, by two 



trunks ; and in a few Fishes, as 



Clupea, Coitus, and certain Cy- 



prinoids, by three or more trunks. 



The pulsatile sac in the Eel, 



309, is situated near the 



beginning of the cardinal vein 



on the ha3mal side of the caudal 



vertebra) at the end of the tail. 



It is of a yellowish colour, 



309 



fig. 



Caudal venous heart of Eel : magn. 20 dlam. 



CCLXIV. 



