196 MORPHOLOGY OF THE ORGANS OF VERTEBRATES. 



portal blood returns to the heart by way of 

 the postcava, while the posterior cardinals 

 merely receive that which comes back from 

 the body walls by way of the intersegmental 

 veins. 



In the amniotes, a renal portal system 

 never reaches that development seen in the 

 ichthyopsida, and is only found in connec- 

 tion with the Wolffian body, i.e., in embry- 

 onic life. When first formed, blood is 

 returned from the kidney by the posterior 

 cardinal veins ; and these extend back and 

 receive the iliac veins as well, no interrenal 

 vein being formed by the co-operation of 

 caudal and postcardinal veins. When the 

 postcava extends back as far as the per- 

 manent kidneys, it sends a renal vein to 

 each ; and from this point backwards it- ab- 

 sorbs the right postcardinal, while on the 

 other side lateral veins extend out and take 

 the blood formerly brought to the postcar- 

 dinal of the left side by the intersegmental 

 FIG. 207. Venous ve i ns> pjg 2O g Q 

 trunks of man. a, azy- . . 



gos; f , caudal (sacralis Farther in front a transverse vein arises 

 media); fi, common from the right postcardinal, and crosses 

 iliac ;, external iliac; ove r and unites with the left, which now 



ej, external jugular; f. , . ,. ,, ,1 j ^ 



. . , loses its connection with the ductus Cu- 



femoral ; g, genital ; ha, 



hemiazygos (azygos vierii and becomes the hemiazygos vein, the 

 minor); Ay, hypo- blood from which now passes across into 

 gastric; ii, internal the . ht cardina l, called in man the 



iliac; ij, internal jugu- 

 lar; k, kidney; ii, left azygos or azygos major. In this way all of 

 innominate; /, pre- the blood from the hinder half of the body 



cava; pk, phrenic;/*, ,; from the kidneys and behind) flows 

 postcava; r, renal; n, ^ 



right innominate; back to the heart through the postcava. 

 5r,subclavian;5r, supra- The anterior portion of the left posterior 

 renal; si, superior in- card i na i may re tain its connection with the 



tercostal; t, thyroid. . ... 



anterior veins (left innominate) of the same 

 side, and become converted into a superior intercostal vein. 



