DIVISIONS OF THE POSTCAVA. 357 



side of the postcava. The left is slightly cephalad of the riglit, and 

 both veins usually lie caudad of the corresponding arteries (Fig. 103). 

 The left renal vein usually receives the Y. spermatica and nearly 

 always contains a pair of valves just centrad of the entrance of the 

 Y. spermatica. The right may also contain valves, but it rarely 

 receives the Y. spermatica dextra. Both often receive the Y. adreno- 

 lumbalis. The Y. renalis, like the A. rcTialis, may be double (§ 969). 

 Finally, when the postcava is divided sufficiently far cephalad 

 (§ 962), the F. renalis may empty into the corresponding division 

 instead of into the postcaval trunk. 



§ 960. V. spermatica (male), ovarii (female), (Fig. 101). — The left opens almost inva- 

 riably into the left renal (§ 959), while the right nearly always empties directly into the 

 postcava. Both are guarded by a pair of valves about 5 mm. from their mouth. 



The V. spermatica returns blood from the testis, and hence passes nearly longitudinally 

 cephalad through the inguinal ring (§ 768) to the point where it empties. It is very slen- 

 der and must be traced with great care. The Y. marii is much shorter, passes obliquely 

 laterad from the ovary, and increases greatly in size during gestation. 



§ 961. V. ilio-lumbalis (Fig. 101). — This enters the postcava at right angles nearly 

 opposite the Crista ilii (Fig. 51). It returns blood from the free or ventral surface of the 

 muscles in this region. 



Divisions of the Postcava. — Usually the postcava is a single 

 median vessel until it reaches a point opposite the junction of the 

 6th and 7th lumbar vertebrae. Here it lies between the aorta and 

 the spinal column ; hence the aorta should be removed. But this 

 part of the dissection should be deferred until the arteries have 

 been studied (§ 965). 



§ 962. Branches :— V. iliaca communis (Fig. 101, A).— The post- 

 cava in the cat is formed by two equal trunks opposite the junction 

 of the 6th and 7th lumbar vertebrae. Each trunk is one of the com- 

 mon iliac veins. Sometimes (once in about ten cases) the postcava 

 divides into the common iliacs much farther cephalad, rarely even 

 cephalad of the kidneys. In such cases the postcava is on the ven- 

 tral or lateral aspect of the aorta, never on its dorsal side. 



§ 963. V. iliaca externa (Fig. 101).— This large vessel comes 

 from the leg, passing into the abdomen dorsad of Poupart's liga- 

 ment (Fig. 39). It unites with the following (§ 964) to form the Y. 

 iliaca communis. The vein should be traced peripherad upon the 

 meros. Just as it enters the abdomen there is a pair of valves that 

 usually stop the plaster injection completely. The valves may be 

 easily demonstrated by slitting the vein longitudinaUy and then 

 blowing peripherad with the blow-pipe (Fig. 102, B, 0, § 130). This 



