672 THE BLOOD-VASCULAR SYSTEM 



The transverse cervical veins [vv. transversae colli] receive tributaries cor- 

 responding in distribution to the branches of the transverse cervical artery. 

 They emerge from beneath the trapezius muscle, cross the posterior triangle, and 

 usually terminate in the subclavian vein. They usually terminate as a single vein 

 the orifice of which is guarded by a pair of valves. Occasionally the cephalic vein, 

 or a branch from the cephahc (the jugulo-cephalic), passes over the clavicle to the 

 subclavian. 



III. THE VENA CAVA INFERIOR AND ITS TRIBUTARIES 



All the veins of the abdomen, pelvis, and lower extremities, with the exception 

 of the superior epigastric (p. 666), and ascending lumbar vein (p. 521), which 

 join with the superior caval system, enter directly or indirectly into the vena 

 cava inferior. The veins corresponding to the parietal branches of the abdominal 

 aorta, except the middle sacral vein, open directly into the vena cava inferior; 

 the middle sacral vein only indirectly through the left common iliac vein. Of the 

 visceral veins corresponding to the visceral branches of the abdominal aorta, 

 those which return the blood from the stomach, intestines, pancreas, and the 

 spleen end in a common trunk called the portal vein. 



The portal vein [vena portse] enters the liver and there breaks up into a net- 

 work of smaller vessels somewhat after the manner of an artery. This network 

 contains venous blood, and is moulded upon the tissue-elements of the organ 

 itself. The smaller vessels consist, like capillaries (from which they differ in 

 developmental history) of intima only; they are called sinusoids. The venous 

 blood is returned from the sinusoidal plexus by the hepatic veins which open into 

 the vena cava inferior as that vessel lies in the fossa venae cavse of the liver. 



Of the other visceral veins, both renals, the right suprarenal, and the right 

 spermatic or ovarian open directly into the vena cava inferior; whilst the left 

 suprarenal and left spermatic or ovarian are drained through the left renal. 



Two of the superficial veins of the lower part of the anterior abdominal wall, 

 the superficial epigastric and superficial circumflex iliac, enter the great saphenous 

 vein; and two of the deep veins from the like situation, the inferior epigastric and 

 deep circumflex iliac, enter the external iliac vein. The blood in these vessels, 

 however, can flow upward as well as in the normally downward direction. In 

 obstruction of the vena cava inferior they become greatly enlarged, and form, 

 with the superior epigastric vein and with other superficial veins of the thorax 

 with which they anastomose, one of the chief channels for the return of the blood 

 from the lower limbs. 



The veins of the pelvis, which receive the veins from the perinseum and gluteal 

 region, join the hypogastric vein. 



THE VENA CAVA INFERIOR 



The vena cava inferior (fig. 529) is the large vessel which returns the blood 

 from the lower extremities and the abdomen and pelvis. It is formed by the con- 

 fluence of the right and left common iliac veins opposite the body of the fifth 

 lumbar vertebra, ascends in front of the lumbar vertebrae to the right of the ab- 

 dominal aorta, passes through the caval opening in the diaphragm, and ends in 

 the lower and back part of the right atrium of the heart on a level with the lower 

 border of the ninth thoracic vertebra. At its origin it lies behind the right 

 common iliac artery on a plane posterior to the aorta, but as it ascends it passes 

 slightly forward and to the right, reaching a plane anterior to the aorta, and 

 becoming separated from that artery by the right medial crus of the diaphragm 

 and the caudate lobe of the liver. While in contact with the liver it lies in a 

 deep groove [fossa venae cavae] on the posterior surface of that organ, the groove 

 being often converted into a distinct canal by a thin portion of the hepatic sub- 

 stance bridging across it. As it passes through the diaphragm its walls are 

 attached to the tendinous margins of the caval opening, and are thus held apart 

 when the muscle contracts. On the thoracic side of the diaphragm it lies for about 

 1.2 cm. (^ in.) within the pericardium, the serous layer of that membrane being 

 reflected over it. 



