SANGUIFEROUS SYSTEM. 477 



the heart. The posterior commencement of this venous 

 trunk in the eel was observed by Hall to present a small 

 pulsating muscular sinus, which accelerates the flow of the 

 blood towards the abdomen. The venous blood received 

 from the upper cutaneous and muscular parts of the coccyx, 

 is conveyed by numerous lateral branches into a superior 

 caudal vein, contained within the upper rings of the vertebrae, 

 and above the spinal chord in the same canal. The lobu- 

 lated kidneys extending along the whole abdomen to the 

 head, exterior to the peritoneum, and attached by cellular 

 substance and vessels to the sides of the bodies of the verte- 

 brae, receive numerous branches, and nearly the whole blood of 

 this superior caudal vein extending forwards above the spinal 

 chord. This venous blood transmitted through the lobes of 

 the kidneys by the superior vein, is received from the capil- 

 laries by lateral descending branches, which convey it into 

 the inferior venous trunk, to be carried forward to the sinus 

 venosus, thus forming a renal portal circulation, like the 

 portal circulation of venous blood through the liver. But 

 the posterior part of this vein also communicates, by direct 

 branches, with the inferior caudal vein. 



The venous blood collected from the chylopoietic viscera of 

 the abdomen, is sent to be distributed through the large and 

 divided liver by a variable number of trunks, forming so many 

 venseportse; and sometimes the long lobes of the liver, attach- 

 ed between the turns of the intestine, receive the separate venae 

 portee more directly from the mesenteric veins. Sometimes only 

 a part of the venous blood from the viscera is conveyed through 

 the liver, and a part is transmitted to the vena cava, as by a 

 ductus venosus in higher embryos. The lungs of fishes, as 

 in the embryos of higher classes, not being employed for 

 respiration, they are nourished by the great visceral artery, 

 like other organs of the abdomen, and their venous blood is 

 transmitted by the portal veins through the liver, or some- 

 times is carried directly to the vena cava. This is a more 

 simple form of the hepatic portal circulation than is found in 

 higher classes, where these visceral venous trunks generally 

 unite to form one great vena portse before entering the liver, 

 and it more resembles the divided condition of the venous 

 portal circulation through the kidneys of fishes. In the 

 thynnus vulgaris Eschricht observed the liver to be composed 



