TEE POSTMBIOB VENA CAVA. 617 



Article III.— PosTEEioK Vena Cava. (Figs. 258, «; 259,/; 293.) 



This vein, whose volume is uot equalled by that of any other vessel in 

 the body, commences at the entrance to the pelvis by two large roots, the 

 pelvi-crural trunks. 



From this point it is directed forward, beneath the bodies of the lumbar 

 vertebrae, soon reaches the superior border of the liver, where it leaves the 

 lumbar region to lodge itself in the fissure excavated on the anterior face 

 of that gland ; passing through this, it traverses the aponeurotic centre of 

 the diaphragm, and opens into the postero-external part of the right auricle 

 of the heart. 



In this course, the posterior vena cava is naturally divided into three 

 portions — a sublumbar, hepatic, and thoracic. 



The sublumbar portion, placed to the right of the abdominal aorta and to 

 the left of the right kidney and suprarenal capsule, is maintained against 

 the common inferior vertebral ligament and the left small psoas muscle by 

 the peritoneum and the pancreas. It responds, besides, to the right renal 

 artery, which crosses its face perpendicularly, as well as the corresponding 

 great splanchnic nerve and the nervous divisions of the right renal and 

 lumbo-aortic plexuses. 



In its hepatic portion, the posterior vena cava is only related to the liver 

 and diaphragm, which form a, complete canal around it. 



The thoracic portion is lodged between the right lung and its internal 

 accessory lobule, and enveloped by a particular serous fold — a dependency 

 from the right pleura, and which has been already described (page 465). 



Collateral afferents. — Those vessels which, as considerable as they are 

 numerous, open into the posterior vena cava, are, enumerating them from 

 before to behind : 



1. The diaphragmatic veins. 



2. The vena portce, a trunk into which are collected the majority of the 

 visceral abdominal veins, and which, instead of opening directly into the 

 vena cava, is divided in the liver like an artery, reconstituting itself 

 into a certain number of thick branches — the suprahepatic vessels, which 

 enter the vena cava on its way through the anterior fissure of the liver. 



3. Menal veins. 



4. Spermatic veins. 



5. Lumbar veins. • 



All these vessels will be studied, in the order above indicated, before the 

 roots or pelvi-crural trunks of the vena cava. 



DIAPHEAGMATIO VEINS. 



These are two, sometimes three, enormous vessels lodged in the texture of 

 the aponeurotic centre, commencing by several branches in the fleshy portion 

 of the muscle, and entering the vena cava at the moment when it traverses 

 the diaphragm. 



VENA PORTa:. (Figs. 293 ; 294.) 



The manner in which this vessel comports itself gives it an altogether 

 peculiar physiognomy, and has caused it to be considered as a separate 

 vascular system. After what has been already said concerning the structure 

 of the liver, it cannot be ignored that the vena portae is distributed in 

 that gland exactly like an artery. 



