768 



THE VASCULAR SYSTEMS 



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

 formation of two pairs of veins, the subcardinal and supracardinal veins (Figs. 548 and 549), and 

 with the ductus venosus. The subcardinal veins lie parallel to, and ventrad of, the postcardinal 

 veins and orginate as longitudinal anastomosing channels which communicate with the post- 



Sinus venosus 



Precardinal 

 Subclavian 



Duct of Cuvier 

 Vitelline 

 Umbilical 

 'ostcardinal 



Subcardinal 

 Renal 



External iliac 

 Internal iliac 



Internal jugular 

 External jugular 

 Subclavian 



Duct of Cuvier 



Left postcardinal 

 Ductus venosus 



Renal 

 Subcardinal 



External iliac 

 Internal iliac 



FIG. 547. Scheme of arrangement 

 of parietal veins. 



FIG. 548. Scheme showing early stages of 

 development of the inferior vena cava. 



cardinals above and below and also by a series of transverse channels. Of the transverse chan- 

 nels, only one persists to join each renal vein. The left subcardinal vein practically disappears, 

 while the right subcardinal enlarges and joins the ductus venosus cephalad and the right 

 postcardinal caudad. At this stage the blood draining the lower extremities passes along a 

 right-sided channel which courses ventrad of the ureter. 



Internal 

 jugu 



Subclavian 



Subclavian 



Renal 

 Spvrmatie 



Suprarenal 

 R&nal 

 Spearma&Te 



FIG. 549. Diagram illustrating the development of the inferior vena cava in the cat. The cardinal and 

 subcardinal veins and dustus venosus are blue and the supracardinal black. (Adopted from McClure and 

 Huntingdon.) 



The supracardinal veins develop as bilaterally symmetrical channels dorsomesad of the 

 postcardinals, by longitudinal anastomoses between parietal postcardinal tributaries (Huntington 

 and McClure). Each vein extends from where the" posterior limb veins open into the post- 



