594 



COMPARATIVE ANATOMY. 



line of the abdomen, and receives veins from the so-called urinary 

 bladder (A, o), after which it is united with its fellow of the opposite 

 side to form a single trunk which passes to the liver, and which is 

 therefore connected with the portal system (a) ; this is the epigastric 

 (abdominal) vein. The veins of the digestive canal and of the spleen 

 are united into a portal trunk, which breaks up in the liver. 



In the Reptilia also the hepatic and the efferent renal veins form 

 an inferior vena cava (B, ci), which opens into the common venous 

 sinus below the right superior cava. But there are various modifi- 

 cations in the different divisions of the Reptilia, and it is in the 

 Saurii and Ophidii only that there is any close similarity to the 

 arrangement of the venous system which obtains in the Amphibia. 

 The caudal vein divides into two trunks, which receive the veins from 

 the hinder extremities in the Saurii, and form the vena3 renaj.es 



Fig. 338. Posterior portion of the venous system. A Of the Frog. B Alligator. 

 C Bird. R Kidneys, c (azygos trunk) Caudal vein, c Crural, i Ischiac vein. 

 v Venae vesicales. a Epigastric (abdominal) vein, m Vena coceygeo-mesenterica. 

 ra Vena renalis advehens. rr Vena renalis revehens. ci Vena cava inferior, h (in 

 A and C) Vena hypogastrica, (in B) End of the epigastric vein in the liver. 



advehentes. The veins of the vertebral column are connected with 

 these. Similar arrangements obtain in the Crocodilini, where the 

 caudal vein (B, c) is also divided, but this vessel then forms a transverse 

 trunk which gives off the venae renales advehentes (ra). In all these 

 forms the venas renales revehentes form a trunk which runs in front 

 of the vertebral column, and there is a renal portal system in the 

 kidneys ; this appears to be absent in the Chelonii only. 



Another venous tract in the Reptilia is represented by the vena3 

 epigastricse sive abdominales. When the allantois is developed, 

 a pair of veins is developed from the vascular network that ac- 

 companies it, and this primitively opens at the same point as the 



