216 THE CAT. [CHAP. vn. 



unite to form a subcutaneous network, which ends in two main 

 channels. The larger of these, the sapJicnous vein, runs up the 

 inner side of the foot, leg, and thigh, beneath the skin, and 

 terminates in the femoral vein. 



The veins of the toes, hind-foot, and leg, also unite to form a deep 

 set of veins, which accompany the arteries as vencB comitcs, and 

 which are more richly supplied with valves than the superficial 

 veins. The various tributaries ultimately unite to form the 

 FEMORAL VEIN, which, as it passes beneath Poupart's ligament 

 with the femoral artery, assumes the title of EXTERNAL ILIAC 

 VEIN. 



Meantime, the small veins of the pelvic viscera unite into larger 

 vessels, generally corresponding with the divisions of the internal 

 iliac artery (except that there is no remnant of any foetal venous 

 structure, save that going to the liver as the " round ligament"), 

 and ultimately unite in a large valveless vessel called the INTERNAL 

 ILIAC VEIN. The external and internal iliac veins unite to form a 

 single vessel the vena cava inferior. 



This VENA CAVA INFERIOR is very much, longer than the superior 

 vena cava, and advances on the right side of the descending aorta. 

 It then bends downwards, perforates the diaphragm, and ends in the 

 right auricle. As it advances from its origin it receives important 

 accessions, corresponding, to a certain extent, with branches directly 

 given off from the abdominal aorta. They are : 



The caudal vein, which, is really the posterior commencement of 

 the lower vena cava, as the caudal artery is the real termina- 

 tion of the aorta. 



The lumbar veins. 



The phrenic veins. 



The spermatic veins. 



The renal veins. 



The capsular veins. 



All these sets of veins correspond with the similarly-named 

 arteries, but there are no veins entering the vena cava which 

 correspond with the superior and inferior mesenteric arteries, or 

 with the cceliac axis, but veins enter it directly, which are called 

 hepatic, though they do not correspond, either in situation or distribu- . 

 tion, with the hepatic artery. They do not correspond in situation, 

 because they enter the vena cava anteriorly to the point at which 

 the ccoliac axis (of which the hepatic artery is a branch) quits the 

 aorta. They do not correspond in situation, because the hepatic 

 artery enters the liver at its transverse fissure, and ramifies in the 

 portal canals, while the hepatic veins run in quite differently directed 

 channels, and converge to the groove in the dorsal margin of the 

 liver, in which lies the vena cava, into which vessel they directly 

 empty themselves. The hepatic veins are valveless. 



23. The veins which correspond with the mesenteric arteries, 

 and with the branches of the ccoliac axis, constitute the PORTAL 

 SYSTEM. Thus we have the superior and inferior mesenteric veins, 



