DISSECTION OF THE ABDOMEN. 333 



The Posterior Vena Cava (Plates 43, 44, 45). This great venous 

 trunk is formed to the right of the termination of the aorta, by the 

 union of the two common iliac veins. It passes forwards along the 

 right side of the lumbar vertebral bodies, until it reaches the upper 

 border of the liver. Here it descends in the anterior fissure of the 

 liver, being included between that organ and the diaphragm. Passing 

 through the foramen dextrum, it enters the thorax. It is related on 

 its left side to the aorta ; and on its right to the psoas parvus, ureter, 

 kidney, suprarenal body, and lumbar sympathetic cord of the same 

 side. It receives the following branches : — 



1. Lumbar Veins, exactly corresponding to the arteries. 



2. Phrenic Veins, or sinuses (2). These begin in the muscular rim 

 of the diaphragm, and converge to the foramen dextrum, where they 

 join the vena cava. They are distinctly visible without dissection in 

 the tendinous centre of the diaphragm (Plate 45). 



3. Spermatic Veins {Ovarian in the mare). The right and left veins 

 often unite before joining the vena cava. 



4. Renal Veins, the left longer than the right. 



5. Hepatic Veins. These join the vena cava while it lies in the 

 anterior fissure of the liver. They discharge the blood of the portal 

 system of veins, after it has circulated in the liver. 



Iliac Veins. There are external and internal iliac veins, with 

 branches corresponding in all respects to the divisions of the homony- 

 mous arteries. The external and internal iliac veins of each side, 

 however, unite and form a short trunk termed the common iliac vein, 

 which is placed in the angle of separation between the external and 

 internal iliac arteries. The right and left common iliac veins unite to 

 form the posterior vena cava. 



The Receptaculum Chyli. Separate the aorta and vena cava at the 

 origin of the anterior mesenteric artery, and look above them for this. 

 It is the dilated commencement of the thoracic duct. It is formed by 

 the union of a variable number of large lymphatic vessels, and it is 

 continued forwards by the duct. The latter is a thin-walled vessel of 

 small calibre which passes into the thorax between the pillars of the 

 diaphragm, being generally to the right of the aorta. 



Last Dorsal and First Two Lumbar Nerves (Plates 44 and 45). 

 The inferior primary branches of these nerves appear at the outer edge 

 of the psoas magnus, the last dorsal being close behind the last rib, and 

 the other two issuing in series behind it. These nerves have already 

 been followed in the dissection of the abdominal wall, where they are 

 distributed in the region of the flank to the abdominal muscles, panni- 

 culus, and skin. These lumbar nerves also furnish cutaneous branches 

 to the inside and front of the thigh. 



3rd Lumbar Nerve (Plates 44 and 45). The inferior primary branch 



