VEINS 



3^2 



of the same side, but in the adult the opening may shift to the Cuvier- 

 ian duct or to the jugular. The common iliac vein likewise empties 

 into a vein, the epigastric or lateral abdo minal, w hich r uns forward 

 in the bod y wall to connect with either the postcardina l or the duct 

 of Cuvier (fig. 332, A). This condition obtains throughout life in 

 some elasmobranchs, but higher in the scale the iliac vein, while 

 retaining its connexion with the epigastric, grows toward the middle 

 line and joins the postcardinal of the same side, a condition which 



Fig. 333. — Development of postcaval system in birds (A, B, sparrow; C, D, chick), 

 schematized after A. M. Miller. In A the postcardinals have extended nearly to the 

 pelvic region and the subcardinals are appearing as isolated spaces. In B the sub- 

 cardinal spaces are uniting and the capillary system connecting with the postcardinals 

 is developing, while the postcava is arising. In C the postcava has united with the 

 subcardinal of the right side, at, ischiadic artery; ate, external iliac artery; au, umbilical 

 (hypogastric) artery; da, dorsal aorta; m, mesonephric veins; om, omphalomesenteric 

 artery; p, postcava and its anlagen; sc, subcardinal and its elements; vet, external iliac 

 vein; vi, ischiadic vein. 



is permanent in amphibia and reptiles (fig. 332, B, C), where blood 

 coming from the hind limb has two routes to the heart. 



The epigastric veins of the two sides may fuse in the median line 

 in front (amphibia, some reptiles, birds), forming an anterior ab- 

 dominal vein (fig. 332, C) which reafiliesJhe heart by pas sing t hrough 

 thexoma ins of t he ventral n ii esente ryj^ligamenttim teres) to the liver 

 and thence forward. A similar anterior abdominal vein has been 

 described in Echidna but is unknown elsewhere in the mammals. 



In the fishes the vessels of the appendages are but slightly de- 



