690 THE BLOOD-VASCULAR SYSTEM 



The femoral vein [v. femoralis], the continuation of the popliteal upward, 

 extends from the tendinous opening in the adductor magnus to the inguinal 

 ligament. In this course its relations are similar to those of the femoral artery. 

 As the vein passes through the adductor canal, it lies behind and a little lateral 

 to the arterj'. At the apex of the femoral trigone (Scarpa's triangle) it is still 

 posterior to the artery, but gradually passes to the medial side as it ascends 

 through the trigone (fig. 541). 



In the neighbourhood of the inguinal ligament the femoral vein lies on the same plane as 

 the artery' from which it is separated by a delicate prolongation of the fascia stretching be- 

 tween the front and back layers of the femoral sheath. On the medial side the vein is sepa- 

 rated by a similar septum from the femoral canal. The femoral vein contains five pairs of 

 valves. 



Tributaries. — The femoral vein receives (in addition to the great saphenous 

 vein, and, in some cases the superficial veins of the epigastrium and groin) the 

 profunda veins and a variable number of small femoral venae comitantes. 



The profunda femoris veins [vv. profunda femoris] arise from the venae comitantes corre- 

 sponding to branches of the profunda femoris artery. The medial and lateral circumflex veins 

 [w. circumflex femoris mediales et laterales] collect blood from the muscles of the adductor 

 and lateral rotator regions. The perforating veins anastomose with femoro-popliteal and other 

 veins of the posterior femoral region, and with the circumflex and accessory popliteal veins. 

 They return blood from the femur and the adductor, hamstring and vasti muscles. 



The venae comitantes, much smaller than the main femoral vein, accompany the femoral 

 artery on either side. They anastomose with one another, with the femoral, and often with the 

 popliteal vein. They terminate in the femoral a short distance above the profunda veins. 



MORPHOGENESIS AND VARIATIONS OF THE VEINS 



The veins of the adult human body tend to accompany the arteries; this tendency is more 

 pronounced in the trunk, neck, and extremities than in the cranium. Developmental history 

 shows that the primitive distribution of the veins of the trunk resembles that of the arteries 

 of the same region in its bilateral symmetry only. Also that the changes which modify the 

 primitive bilateral symmetry of the chief veins are not only more extensive but of a different 

 nature from those producing a similar effect upon the arteries. In both cases the main body- 

 vessels begin as a pair of main longitudinal trunks and end as a main unpaired channel (or 

 channels in the case of the venous system) situated near the median plane of the body. In 

 the case of the venous system the change results from wholesale destruction of the vessels on 

 the left of the body accompanied by enlargement of those upon the right. In the arterial 

 system destruction occurs to a much more limited extent; the definitive channel results mainly 

 from blending of the two primitive aortse. 



The main venous channels of the cranium and extremities are primitively superficial; 

 in the cranium they remain so. In the extremities new veins are formed which follow the main 

 arteries; to these the more primitive channels become tributary. 



The heart, as soon as it assumes the simple tubular form is found to receive four veins. 

 These, the two vitelline and two umbilical veins, enter the sinus venosus, a vitelline and an 

 umbilical vein on either side. The umbilical veins are lateral to the vitellines, and are paired 

 within the body only; they arise from the placenta, and traverse the belly-stalk as a single 

 trunk. The vitelline veins return blood from the yolk sac, and, at first, are independent 

 throughout. 



At a later period two other pairs of veins arise for the venous drainage of the embryonic 

 body. They are the pre- and post-cardinals which drain the cephalic and caudal regions 

 respectively. The right pre-cardinal vein unites with the right post-cardinal to form the right 

 common cardinal (duct of Cuvier). The latter runs in a medial direction to join the sinus 

 venosus lateral to the right umbilical. On the left side the arrangement matches that on the 

 right to produce a primitively symmetrical pattern. 



During development changes are brought about in the primitive veins which end in the 

 pro(hiction of the adult venous system as follows: the common and pre-cardinals, together 

 witli the subclavian veins and the cephalic ends of the post-cardinals, are transformed into the 

 vena cava superior and its larger tributaries. The remainder of the post-cardinal system is 

 instrumental in the production of the vena cava inferior and its tributaries. Finally the 

 intra-embryonic portions of the vitelline and umbilical veins participate in the formation of the 

 portal and hepatic systems of veins together with the proximal end of the vena cava inferior. 



The following brief account of morphogenesis and variations is divided into three headings 

 (1) vena cava .superior and its tributaries; (2) vena cava inferior and its tributaries, and (3) 

 the portal system. 



A. THE VENA CAVA SUPERIOR AND ITS TRIBUTARIES* 



1. MORPHOGENESIS 



Tlio pre-cardinal vcin.s at first return ])loo(l from the head only, but as the heart recedes 

 into the thorax the cardinal veins migrate with it. In so doing the common cardinals lag 

 somewhat behind and in consequence tlieir direction, primitively transverse, approaches the Ion- 



