Anteriorly the postcardinal channel is involved. The renal 

 portal blood is also received from the segmentals of the body 

 wall. In some teleosts, the left subcardinal is much reduced 

 and the right is more strongly developed. This resembles 

 the situation in the dipnoan, but it differs in that a post- 

 caval stem does not develop. 



Development within the actinopterygian group shows ex- 

 treme variation, but the general pattern is that seen in the 

 higher groups. There are paired subcardinal stems, lying 

 medial to the nephric ducts which lead from the caudal 

 vein. The latter connects to either side of the anus with a 

 subintestinal channel (of bilateral origin) which bifurcates 



external jugular 



B 



U external jugular 

 brachiocephalic 



subclavian 



sinus venosus 



renal sinus 



renal portal 



ventral abdominal 



f ¥ 



aortic arches 

 3rd 4th 5th 6th cutaneous artery 



anterior cardinal 

 (internal jugular) ~^ 



external jugular 

 (inferior jugular) 



anterior cerebro 



basilar artery 

 sinus venosus- 



internal carotid 

 external carotid 



Figure 1 1-39. Development of the posterior vonous pattern of an anuran. A, the circulatory sys- 

 tem of an early larval frog (about 4.6 mm); B to E, four stages in the development of the veins in 

 Bufo. (A after Adamstone and Shumway, 1947) 



CIRCULATION IN THE BODY 



371 



