CIRCULATORY SYSTEM. 217 



the conduit returning tlie blood from the parietes of the abdomen 

 and pelvis, the urinary and genital organs, and the posterior ex- 

 tremities. The internal and external iliac veins, unlike their ac- 

 companying arteries, coalesce and form two common iliac trunks, 

 from the subsequent union of which, upon the last vertebra of the 

 loins, results the main trunk now under consideration. Thus 

 formed, it takes its course underneath the bodies of the lumbar 

 vertebree, runs within the great fissure of the liver, perforates the 

 chordiform tendon, and pursues its way directly across the middle 

 space of the cavity of the chest to the posterior and inferior part 

 of the right auricle. In its passage it is joined by the lumbar, 

 spermatic, renal, hepatic, and diaphragmatic veins. 



The lumbar veins, correspondent in number and course to 

 the lumbar arteries, result from the union of small veins issuing 

 from the muscles clothing the loins ; receiving in their subsequent 

 passage, each of them, a branch emerging from the vertebral 

 canal; and ultimately joining the main trunk at right angles. 



The spermatic vfIxN ascends alongside of its artery, pur- 

 sues its course forward within the abdomen, and terminates in the 

 under side of the posterior vena cava ; in some instances, uniting 

 first with its fellow into one common vessel. 



The renal or emulgent vein, formed by a combination 

 of branches emerging from the pelvis of the kidney, which com- 

 monly exceed in number the divisions of the artery, accompanies 

 the renal artery to the spine, and ends in the under and outer 

 part of the main trunk. The left vein is longer than the right, in 

 consequence of having to cross the aorta. They also receive the 

 veins belonging to the capsuloe renales. 



The hepatic veins, manifold in number, spring from the 

 terminations of the vena portae and hepatic artery, issue from the 

 parenchyma of the liver, and end in the vena cava, as it runs 

 along the great fissure, by numerous orifices resembling pinholes. 



The phrenic or diaphragmatic veins. From the arbo- 

 rescent venous display upon the surface of the diaphragm result 

 six ascending branches of considerable size ; these, however, con- 

 join afterwards, and make but two on each side, which enter the 

 trunk as it perforates the tendinous substance. 



The Common Iliac Veins 

 Take their rise under the sacro-iliac symphysis from the union 

 of the external with the internal iliacs. Their course, which is 

 very short, is obliquely forward under the last vertebra of the 

 loins, where they coalesce and form the main trunk. They re- 

 ceive, however — 1. A considerable vein resulting from the con- 

 junction of small branches coming from the psose and iliacus, 



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