330 



COMPARATIVE ANATOMY 



and are replaced by vertebral veins, while in Mammals they persist 

 as the azygos veins. An anastomosis is formed between these, and 

 eventually the anterior part of the left disappears, the blood from 

 both sides passing into the right azygos (hemiazygos), which opens 

 into the right precaval (Figs. 269 and 270). 



The anterior cardinals give rise, as in lower Vertebrates, to the 

 jugulars, which, as well as the subclavians and vertebrals or azygos, 



FIG. 269. DIAGRAM SHOWING THE RELATIONS OF THE POSTERIOR CARDINAL 



AND POSTCAVAL VEINS IN A, THE RABBIT, AND B, MAN. (After Hoch- 



stetter). 



V.r.d, V.r.s, renal veins ; V.d.s.e, common iliac vein ; VI. I, lumbar vein ; V.c.i, 

 postcaval ; V.c.p.d, V.c.p.s, right and left posterior cardinals ; V.il.int.comm, 

 common internal iliac vein. 



open into the precavals. In Reptiles, Birds, Monotremes, and 

 Marsupials, as well as in many Rodents, Insectivores, Bats, and 

 Ungulates, both precavals persist throughout life ; but in other 

 Mammals the main part of the left disappears, all the blood from 

 the head and anterior extremities passing into the right. The 

 coronary veins open into the base of the left precaval (coronary 

 sinus, Fig. 259). 



