520 



ANGIOLOGY 





vein and the ductus venosus undergo atrophy and obliteration after birth, ard 

 form respectively the ligamentum teres and ligamentum venosum of the liver. 



The Parietal Veins. The first indication of a parietal system consists in the 

 appearance of two short transverse veins, the ducts of Cuvier, which open, one 

 on either side, into the sinus venosus. Each of these ducts receives an ascending 

 and descending vein. The ascending veins return the blood from the parietes 

 of the trunk and from the Wolffian bodies, and are called cardinal veins. The 

 descending veins return the blood from the head, and are called primitive jugular 

 veins (Fig. 477). The blood from the lower limbs is collected by the right and 

 left iliac and hypogastric veins, which, in the earlier stages of development, open 

 into the corresponding right and left cardinal veins; later, a transverse branch (the 

 left common iliac vein) is developed between the lower parts of the two cardinal 

 veins (Fig. 479), and through this the blood is carried into the right cardinal vein. 

 The portion of the left cardinal vein below the left renal vein atrophies and dis- 

 appears up to the point of entrance of the left spermatic vein; the portion above 



Sinu* venosus 



Primitive jugular 

 Subdavian 



Duct of Cuvier 

 Vitelline 

 Umbilical 

 Cardinal 



Subcardinal 

 Renal 



External iliac 

 Eypogastric 



FIG. 477. Scheme of arrangement of parietal 

 veins. 



Internal jugular 

 External jugular 

 Subdavian 



Duct of Cuvier 



Left cardinal 

 Ductus venosus 



. Renal 

 Subcardinal 



External iliac 

 Hypogastric 



Fio. 478. Scheme showing early stages of 

 development of the inferior vena cava. 



the left renal vein persists as the hemiazygos and accessory hemiazygos veins 

 and the lower portion of the highest left intercostal vein. The right cardinal vein 

 which now receives the blood from both lower extremities, forms a large venous 

 trunk along the posterior abdominal wall; up to the level of the renal veins it 

 forms the lower part of the inferior vena cava. Above the level of the renal veins 

 the right cardinal vein persists as the azygos vein and receives the right intercostal 

 veins, while the hemiazygos veins are brought into communication with it by the 

 development of transverse branches in front of the vertebral column (Figs. 479, 480) 

 Inferior Vena Cava. The development of the inferior vena cava is associated 

 with the formation of two veins, the subcardinal veins (Figs. 477, 478). These 

 lie parallel to, and on the ventral aspect of, the cardinal veins, and originate as 

 longitudinal anastomosing channels which link up the tributaries from the mes- 

 entery to the cardinal veins; they communicate with the cardinal veins above and 

 below, and also by a series of transverse branches. The two subcardinals are for 

 a time connected with each other in front of the aorta by cross branches, but these 

 disappear and are replaced by a single transverse channel at the level where the 



