VEINS OF VERTEBRATA. 595 



ends of the ductus Cuvieri (Ratlike: Ring Snake). These umbilical 

 veins receive veins from the abdominal wall, and are also connected 

 with the formation of the hepatic portal circulation. In the Ophidii 

 this umbilical vein disappears after the veins of the abdominal wall 

 which open into it have broken up into a plexus, but in the Saurii 

 the terminal portion of one umbilical vein persists, and. unites with 

 the abdominal veins that open into it to form an epigastric vein ; this 

 receives veins from the urinary bladder, and passes forwards to the 

 liver. 



In the Crocodilini and Chelonii the ends of the umbilical venous 

 trunks persist, and form, as they are continued into the veins of the 

 abdominal wall, a part of the epigastric veins. Like the single veins 

 in the Amphibia and Saurii they also go to the liver, and, in the 

 Crocodilini, they are connected with branches of the portal vein. In 

 the Chelonii, those of either side unite into a transverse trunk, which 

 receives the various venge intestinales, which are not, in them, united 

 into a portal venous trunk. In both cases they are distributed in the 

 liver, and belong therefore to the portal venous system. In the 

 Crocodilini, as in the Chelonii, the epigastric veins (B, a) are given 

 off from the two branches of the caudal vein (c), and receive the 

 crui^als (c) ; they also receive the ischiac veins more anteriorly. But, 

 since in the Crocodilini, the venae renales advehentes also arise from 

 the caudal vein and its connection with the ischiac vein, part of the 

 venous blood from the hinder portion of the body is carried into the 

 renal portal circulation, and the rest into that of the liver. But in 

 the Chelonii, where there are no advehent renal veins, all the blood 

 from the hinder end of the body is carried into the liver, for the 

 vertebral veins, in these forms, also open into the epigastric veins. 



§ 441. 



Several of the veins which are found in the Reptilia are not 

 permanent structures in Birds. The inferior vena cava (Fig. 338, 

 (7, ci) is indeed still made up of two trunks from the kidneys, but 

 these receive the veins of the hind-limbs (c), and might from their 

 size be taken to be the continuation of these veins. Two hypo- 

 gastric veins (h) are connected with these trunks in addition to the 

 vessels which arise from the kidneys. They are united by a trans- 

 verse anastomosis at the root of the sacrum ; this anastomosis 

 receives the caudal veins (c) from behind, and gives off in front a 

 vena coccygeo-mesenterica (m), which goes to the mesenteric vein. 

 This vena coccygeo-mesenterica is a wide trunk in the Crocodilini 

 also, where it anastomoses with the transverse trunk, which unites 

 the two branches of the caudal vein ; part of the venous blood 

 from the tail or hinder extremities is conducted away from the renal 

 portal circulation by it. 



In the Mammalia there are no indications whatever of a renal 

 portal system. The umbilical and omphalo-mesenteric veins have 

 the same relations as in Reptiles, though there are several variations 



2 q 2 



