VENOUS SYSTEM. 



Mil 



twecn the veins of all parts of the trunk, so 

 that we can suppose one of tiie vena? cav;e to 

 be obliterated without the venous circulation 

 being interrupted. The greater azygos itself, 

 which is generally regarded as the principal 

 means of communication between the two 

 veme cavae, is not, however, nccessarv, when 

 we consider the anv.ngement of the anterior 

 and posterior s- phial plexus'.-s. Thus, I have 

 sometimes seen the inferior, and sometimes 

 the superior vena cava, obliterated without 

 any apparent increase in the diameter of the 

 vena azygos, and, what will perhaps be thought 

 surprising, without oedema either of the 

 upper or lower extremities. 



" Supposing the vena cava ascendens to he 

 obstructed from the entrance of the hepatic 

 veins down to tiie renal veins, the blood 

 would then flow back bv the lumbar veins into 

 the plexuses contained within the spinal canal ; 

 through these plexuses it would ascend to the 

 vertebra-costal (intercostal) veins, from thence 

 to the azygos veins, and through them into 

 the superior vena cava. 



" If all the jugular veins were obliterated, 

 the venous circulation in the head would still 

 continue, and would be carried on through 

 the spinal veins." * 



B. VEINS wiiicn FORM THE INFERIOR 

 VENA CAVA. 



The veins which unite to form the inferbr 

 vena cava transmit the blood which is derived 

 from the lower extremities and from the vis- 

 cera of the pelvis and of the abdomen. 



I. Veins of the lower extremities. The 

 veins of the lower, like those of the upper 

 extremities, are divided into a d^ep and a 

 superficial set ; they are likewise provided 

 with valves, which are most numerous in the 

 veins of the former class. 



Superficial veins of the lower extremities. 

 The small veins, which in great numbers 

 exist in the subcutaneous cellular tissue of the 

 dorsum of the foot, unite to form two prin- 

 cipal trunks termed saphenous. These are 

 placed, the one on the inner, and the other on 

 the posterior aspect of the leg. 



Internal or long saphena vein. This vein 

 first exists as a distinct vessel a little below 

 the ankle joint, in front of which it ascends 

 and passes along the inner surface of the leg, 

 at the distance of half an inch from the inner 

 margin of the tibia. At the knee it lies be- 

 hind the internal condyle, superficial to the 

 tendons of the sartorius, graci'is, and semi- 

 tendinosus muscles, and continuing to ascend 

 on the internal and anterior surface of the 

 thigh, gains the " saphenic opening" in the 

 fascia lata, through which it passes backwards 

 to end in the femoral vein, at the distance of 

 about an inch below Poupart's ligament. 



In this long course the saphena vein re- 

 ceives many cutaneous branch .?, and also 

 several communicating veins from the deep 

 vessels. In the thigh, it is joined, near its 

 termination, by a large branch, which comes 



* Cruveilhier's Descriptive Anatomy, vol. ii. 

 p. 810. 



from the back of the limb, and by two or 

 three veins which are derived from the an- 

 terior and external surfaces of the thigh. 

 These latter pursue a direction upwards and 

 inwards, and thus cross anterior to the 

 femoral artery, so that they are liable to be 

 injured by the incisions made to expose that 

 artery. The trunk of the saphena vein itself 

 is seldom thus endangered, as it ascends on a 

 plane internal to the artery. Shortly before* 

 its termination, the saphena vein is enveloped 

 in the meshes of the cribriform fascia, where 

 it is joined by three cutaneous veins from the 

 parieties of the abdomen, viz. the superficial 

 pubic, the superficial drcwnrftexa i/ii, and the 

 superficial epigastric veins. When, from any 

 cause, the circulation through the inferior 

 vena cava is obstructed, those veins become 

 remarkably enlarged and tortuous. 



The internal saphena vein is accompanied, 

 from the ankle to the knee, by the internal 

 saphena nerve. The valves, in its interior, 

 Vary from two to six sets. 



Communicating branches pass between this 

 vein and the deep veins of the leg and thigh ; 

 they are most numerous in the leg, where 

 they connect the saphena with the anterior 

 and posterior deep tibial veins. 



Posterior or external saphena vein. The 

 external saphena vein is formed by the union 

 of several branches from the outer side of the 

 foot, and ascends into the leg behind the 

 outer ankle. Inclining inwards and upwards, 

 it gains the centre of the back of the leg, 

 passes superficial to the groove between the 

 heads of the gastrocnemius muscle, and enters 

 the poplitaeal region. Opposite the line of 

 flexion of the knee-joint, this vein passes 

 through a small round opening in the popli- 

 taeal fascia, and joins the poplitaeal vein about 

 its centre. This ves>el, sometimes called the 

 short saphena vein, is accompanied in part of 

 its course by the posterior saphena nerve. It 

 is usually furnished with two valves, which 

 are found near the termination of the vessel. 

 This vein communicates but rarely with the 

 deep veins of the leg. 



Deep veins of the lower extremity. In the 

 lower, as well as in the upper extremities, the 

 deep system of veins is represented by the 

 " vena? comites " of the larger arteries. The 

 satellite veins of the posterior tibial artery are 

 derived from the deep plantar iv/ua (external 

 and internal). At the upper part of the leg 

 the posterior tibial veins are joined by the 

 satellite veins of the peroneal, and subse- 

 quently, at the lower edge of the poplila-us 

 muscle, by those of the anterior tibial artery. 

 Bv the union of these is the trunk of the 

 poplitaeal vein formed. 



The pophlfcal vein. This vein is of large 

 size, owing to the number and magnitude of 

 the branches which it receives; it is joined by 

 the tibial veins, by the external sfiphena, by the 

 articular, and, lastly, by imtsrnlar veins of huge 

 size (sitral) from the calf of the leg. 



Thepoplitseal vein is placed posterior to its 

 artcrv below, posterior and a little external to 

 that vessel, at the upper part of the poplitaeal 



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