DEVELOPMENT OF THE VEINS 275 



the common hepatic and right hepatic veins (primitive right vitelline); 

 (2) the vein of the plica venae cavae; (3) an inter-renal portion of the right 

 subcardinal vein with its great mesial anastomosis; (4) the right supra- 

 cardinal vein, below the level of the kidneys. 



The permanent kidneys take up their positions opposite the great anas- 

 tomosis between the subcardinals, and at this point the renal veins are 

 developed (Fig. 282 B); the longer left renal vein differs from the right 

 in that proximally it represents a left portion of the anastomosis itself 

 (Fig. 282 D}. A cephalic portion of the left subcardinal vein persists 

 as the left suprarenal vein, which thus opens into the left renal instead of 

 joining the inferior vena cava as does the right suprarenal vein of similar 

 origin.' The left spermatic or ovarian vein early drains into the left caudal 

 border of the great subcardinal anastomosis, which, as we have seen, 

 contributes to the left renal vein. The right spermatic or ovarian vein 

 opens into the right border of that portion of the subcardinal anastomosis 

 which is incorporated into the inferior vena cava. Thus tjhe', subcardinal 

 veins aid in the formation of the inferior vena cava and the spermatic 

 or ovarian vessels, whereas they constitute all of the suprarenal veins; the 

 rest of the subcardinal system atrophies. 



The lumbar veins develop from the same right supracardinal plexus 

 that gives rise to the caudal segment of the inferior vena cava. Caudal 

 to its lowest transverse connection with its mate (z, Fig. 2826"), the right 

 subcardinal vessel becomes the right common iliac vein. The correspond- 

 ing portion of the similar left vein, plus the transverse anastomosis, 

 becomes the left common iliac vein. The external and internal (hypo- 

 gastric) iliacs persist after the posterior cardinal veins disappear and now 

 join the new common iliacs. 



Veins of the Extremities. The primitive capillary plexus of the upper and lower limb 

 buds gives rise to a border win (Figs. 285 and 322), which courses about the periphery of 

 the flattened limb buds (Hochstetter). In the upper extremity, the ulnar portion of the 

 border vein persists, forming at different points the subclaiiian, axillary, brachial, and basil- 

 ic veins. The border vein at first opens into the dorsal wall of the posterior cardinal vein 

 (embryos of 10 mm.), but, as the heart shifts its position caudalward, it finally drains by a 

 ventral connection into the anterior cardinal, or internal jugular vein (Lewis). The cephalic 

 vein develops secondarily in connection with the ulnar border vein; later, in embryos of 

 23 mm., it anastomoses with the external jugular and finally drains into the axillary vein, 

 as in the adult. With the development of the digits, the w. cephalica and basilica become 

 distinct, as in embryose of 35 mm., but later are again connected by a plexus on the dorsum 

 mani, as in the adult (Evans). 



In the lower extremity, the fibular portion of the primitive border vein persists. Later, 

 the v. saphena magna arises separately from the posterior cardinal, gives off the w. 

 femoralls and tibialis posterior, and annexes the fibular border vein at the level of the knee. 

 Distal to this junction the border vein persists as the i>. tibialis anterior, and, probably, the 

 v. saphena parva; proximally, it becomes greatly reduced, forming the v. glutea inferior. 



