ABNORMALITIES OF THE LYMPHATICS. 905 
THE INFERIOR VENA CAVA. 
The lower part of the inferior vena cava is sometimes absent, in which case the common iliac 
veins ascend, one on the right and the other on the left of the aorta, to the level of the second 
lumbar vertebra, where the left common iliac vein receives the left renal vein, and then crosses in 
front of or behind the aorta to fuse with the right corresponding vein ; in these cases, therefore, the 
inferior vena cava commences at the level of the second lumbar vertebra, and it represents only 
the upper and last-formed part of the ordinary vessel; the common iliac veins, each of which 
receives the lumbar veins of its own side, are exceptionally long, and they may or may not be 
united at the pelvic brim by a small transverse anastomosing channel. 
Occasionally the inferior vena cava does not terminate in the right auricle, but is continuous 
with the vena azygos major, which is much enlarged, all the inferior caval blood being then 
carried to the superior vena cava. In these cases the hepatic veins open directly into the right 
auricle without communicating with the inferior vena cava. 
The lower part of the inferior vena cava sometimes lies to the left instead of to the right of 
the aorta ; this condition is associated with a long right common iliac vein, which crosses obliquely 
from right to left to joim the shorter left common iliac vein. After receiving the left renal vein 
the misplaced inferior vena cava crosses in front of the aorta, reaching the right side at the level of 
the second or first lumbar vertebra. In other cases, however, the left inferior vena cava continues 
upwards through the left crus of the diaphragm, usurping the place of a greater or smaller part 
of the left azygos vein ; having entered the thorax, it may cross to the opposite side and terminate 
in the vena azygos major, or 1t may continue upwards on the same side, and after arching over 
the root of the left lung, descend behind the left auricle, to terminate in the right auricle in the 
situation of the coronary sinus. In this group of cases also the hepatic veins open separately into 
the right auricle. 
The tributaries of the inferior vena cava are also subject to variation. Additional renal, 
spermatic, ovarian, or suprarenal veins may be present. Two or three lumbar veins of one or 
both sides may unite into a common trunk which terminates in the inferior vena cava, and the 
hepatic veins may open separately, or after fusing into a common trunk, into the right auricle 
near the opening of the inferior vena cava. 
No explanation of the variations of the inferior vena cava and its tributaries is necessary, 
beyond the statement that they are due to persistence of portions of the cardinal veins which 
usually disappear, and to the persistence of transverse anastomoses and tributaries which usually 
atrophy, or to modifications of those which ordinarily take part in the formation of the 
inferlor vena caval system. 
The left common iliac vein is short and the right long when the inferior vena cava lies on 
the left side. The common iliac veins may be absent, the internal iliac veins uniting to form the 
commencement of the inferior vena cava, into which the external iliac veins open as lateral 
tributaries. 
THE VEINS OF THE LOWER EXTREMITY. 
The long saphenous vein is not subject to much variation, but the short saphenous vein 
may terminate by joining the long saphenous, or, after piercing the deep fascia in the lower part 
of the thigh, it may ascend and join the sciatic vein or one of the tributaries of the profunda 
vein. 
The vene comites are generally described as terminating in the lower extremity, at ‘the 
lower part of the popliteal space, but they may ascend as far as Scarpa’s triangle; as a matter 
of fact, although as a rule there is only one large popliteal and one large femoral vein, 
one or more small additional veins usually accompany the popliteal and femoral arteries. 
In a few cases the popliteal vein does not pierce the lower part of the adductor magnus, but 
ascends behind that muscle and becomes continuous with the profunda vein, the femoral artery 
being unaccompanied by any large vein during its passage through Hunter’s canal. 
ABNORMALITIES OF THE LYMPHATICS. 
Variations of the glands and smaller vessels of the lymphatic system are so common that 
they can hardly be regarded as abnormalities ; variations of the larger vessels, however, are com- 
paratively rare. This is especially the case with respect to the two terminal trunks, the thoracic 
duct and the right lymphatic duct, the abnormalities of which are interesting and important. 
When the arch of the aorta is on the right instead of on the left side, the thoracic duet 
usually terminates in the right innominate vein, in which case it receives the tributaries which 
usually open into the right lymphatic duct, whilst the corresponding area on the left side is 
drained by lymphatics terminating in a left lymphatic duct which opens into the commencement 
of the left innominate vein. A similar arrangement of the terminal lymphatic trunks sometimes 
occurs even when the arch of the aorta is in its normal position on the left side. In either case 
the thoracic duct may commence in the usual way, and after reaching the level of the fifth dorsal 
vertebra continue upwards on the right side, instead of crossing to the left side, of the vertebral 
column ; more rarely it commences on the left side and crosses over to the right at a higher level. 
In one ease in which the thoracic duct opened into the right innominate vein, instead of the 
left, no trace of a lymphatic duct was discovered on the left side. 
