THE POSTEBIOR VENA CAVA. 703 



to be followed by haemorrhage from the open orifices of these areolae — a circum- 

 stance which does not take place. 



" It does not appear, therefore, that there is, in the structure of the third 

 phalanx, any departure from the general plan on which bones are constructed, 

 and we think that its internal venous system is hmited to the vessels — very 

 numerous as they are — which accompany the arterial divisions." 



Akticle III.— Posteeior Vena Cava (Figs. 349, v ; 350,/; 389). 



This vein, the volume of which is not equalled by that of any other vessel 

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

 common iliac veins. 



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 on the anterior face of that gland ; 

 passing through this, it traverses the foramen dextrum of the diaphragm, and 

 opens into the postero-external part of the right am'icle 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 posterior aorta and to the 

 left of the right kidney and supra-renal capsule, is maintained against the 

 common inferior vertebral hgament and the left psoas parvus muscle by 

 the peritoneum and the pancreas. It is related, besides, to the right renal 

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

 splanchnic nerve and the nerve 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 acces- 

 sory lobule, and is enveloped by a particular serous fold — a dependency from the 

 right pleura, and which has been already described (p. 543). 



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

 rous, open into the posterior vena cava, are, enumerating them from before to 

 behind : 



1. ThQ phrenic or diaphragmatic veins. 



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

 abdominal visceral veins ; instead of opening directly into the vena cava, it is 

 divided in the liver like an artery, reconstituting itself into a certain nmnber of 

 thick branches — the hepatic veins, which enter the vena cava on its way through 

 the anterior fissure of the liver. 



3. Renal veins. 



4. Spermatic veins. 



5. Lumbar veins. 



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

 radicles or common iliac veins of the vena cava. 



Phrenic or Diaphragmatic Veins. 



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

 the tendinous centre, commencing by several branches in the fleshy portion of 

 the muscle, and entering the vena cava as it passes through the diaphragm. 



