efferent vein 



afferent renol channels 



hole in valve diaphragm 

 external iliac 



efferent of onterior lobe 



ischioc 



coccygeomesenteric 

 renal portal channel 



external iliac 



afferent of posterior lobules 



efferent of posterior lobules 



-hypogastric vein 

 -caudal vein 



B 



Figure 11-38. The renal porfal system of the bird. A, with details of the valve between the 

 external iliac and the efferent renal channel. The arrows in A indicate the direction of flow. (After 

 Spanner, 1925) 



the posterior vena caval stem. In the frog, only the post- 

 caval stem is involved in this drainage. 



In the development of the postcardinal drainage of the 

 anuran (Figure 11-39), lateral (postcardinal) and medial 

 (subcardinal) channels of a reticulum enclosing the nephric 

 duct are seen. The medial (subcardinal) channel appears 

 first (10-mm frog). The postcaval stem connects with the 

 right postcardinal. Both postcardinals flow through pro- 

 nephric sinuses to reach the duct of Cuvier (Figure 11-39); 

 these sinuses are eliminated with the loss of the pronephros. 

 The same general pattern appears to hold for the sala- 

 manders. 



Choonafe fishes Prolopterus, described by Parker, has lost 

 the right connection with the duct of Cuvier; this is re- 

 placed by a postcaval stem. The posterior parts of both 

 postcardinals form renal portal vessels which drain the pelvic 

 and caudal veins. Subcardinal channels, interconnected 

 by cross channels, drain the kidneys. The postcava enters 

 the liver and receives the hepatic veins along its course. 

 The hepatic portal system drains the intestine by way of in- 

 traintestinal and subintestinal channels. 



In Neoceralodus the picture differs in that the caudal vein 



flows into the postcava rather than the renal portal veins. In 

 addition, there are both ventral abdominal and lateral cu- 

 taneous veins, connected with the renal portal and caudal 

 veins respectively. 



The development of the circulatory channels oi Neoceralo- 

 dus has been described by Kellicott (1905) and the very 

 early stages oi Lepidosiren by Robertson (1913). In the early 

 embryo, the duct of Cuvier extends down over the yolk sac 

 to reach the heart. Numerous segmentals, of which the duct 

 of Cuvier is one, form a reticulum of channels in the prone- 

 phric area and over the yolk. These drain into the bilateral 

 vitelline veins, which unite posteriorly below the gut as a 

 subintestinal. The subintestinal connects to either side of the 

 anus with the posterior cardinal channels, which, posteriorly, 

 unite to form the caudal vein. 



Neoceralodus follows a similar pattern. The left vitelline be- 

 comes the stem for the subintestinal vein, which is retained 

 in the adult and forms part of the hepatic portal. 



Actinopterygian fishes In the actinopterygian fishes there 

 is a great deal of variation in the posterior cardinal drain- 

 age. The caudal vein enters the kidney by way of the sub- 

 cardinal channels; these mav be fused at the midline. 



370 



THE CIRCULATORY SYSTEM 



