616 THE BLOOD-VASCULAR SYSTEM. 



heads of the Gastrocnemius it is superficial to that vessel ; but above the knee- 

 joint it is close to its outer side. It receives the sur.al veins from the Gastro- 

 cnemius muscle, the articular veins, and the external saphenous. The valves in 

 this vein are usually four in number. 



The Femoral Vein accompanies the femoral artery through the upper two- 

 thirds of the thigh. In the lower part of its course it lies external to the artery ; 

 higher up it is behind it; and at Poupart's ligament it lies to its inner side and 

 on the same plane. It receives numerous muscular tributaries, and about an inch 

 and a half below Poupart's ligament it is joined by the profunda femoris ; near its 

 termination it is joined by the internal saphenous vein. The valves in this vein 

 are four or five in number. 



The External Iliac Vein commences at the termination of the femoral, beneath 

 the crural arch, and, passing upward along the brim of the pelvis, terminates 

 opposite the sacro-iliac synchondrosis by uniting with the internal iliac to form 

 the common iliac vein. On the right side it lies at first along the inner side of 

 the external iliac artery, but as it passes upward gradually inclines behind it. 

 On the left side it lies altogether on the inner side of the artery. It receives, 

 immediately above Poupart's ligament, the deep epigastric and deep circumflex 

 iliac veins and a small pubic vein, corresponding to the pubic branch of the 

 obturator artery. According to Friedreich, it frequently contains one, and some- 

 times two valves. 



The Deep Epigastric Veins. Two veins accompany the deep epigastric artery ; 

 they usually unite into a single trunk before their termination in the external 

 iliac vein. 



The Deep Circumflex Iliac Veins. Two veins accompany the deep circumflex 

 iliac artery. These unite into a single trunk which crosses the external iliac 

 artery just above Poupart's ligament and terminates in the external iliac 

 vein. 



The Internal Iliac Vein is formed by the venae comites of the branches of the 

 internal iliac artery, the umbilical arteries of the foetus excepted. It receives the 

 blood from the exterior of the pelvis by the gluteal, sciatic, internal pudic, and 

 obturator veins, and from the organs in the cavity of the pelvis by the haemor- 

 rhoidal and vesico-prostatic plexuses in the male, and the uterine and vaginal 

 plexuses in the female. The vessels forming these plexuses are remarkable for 

 their large size, their frequent anastomoses, arid the number of valves which they 

 contain. The internal iliac vein lies at first on the inner side, and then behind the 

 internal iliac artery, and terminates opposite the sacro-iliac articulation by uniting 

 with the external iliac to form the common iliac vein. This vessel has no valves. 



The internal pudic veins (vence, comites} have the same course as the internal 

 pudic artery. They receive tributaries corresponding to the branches of the 

 artery, except the tributary corresponding to the dorsal artery of the penis ; that 

 is, the dorsal vein of the penis, which opens into the pro-static plexus. 



The haemorrhoidal plexus surrounds the lower end of the rectum, being formed 

 by the superior haemorrhoidal veins, tributaries of the inferior mesenteric. It 

 commences as a series of dilated pouches, about twelve in number, which are 

 arranged circularly at the verge of the anus and are connected by transverse 

 branches. From these pouches veins, about six in number, pass upward in a, 

 straight direction in the submucous tissue for about three inches ; they then pierce 

 the muscular coat and become arranged in a circular manner at right angles to the 

 long axis of the gut, and eventually unite to form the superior haemorrhoidal vein. 



Surgical Anatomy. The veins of this plexus are apt to become dilated and varicose, and 

 form piles. This is due to several anatomical reasons : the vessels are contained in very loose, 

 lax connective tissue, so that they get less support from surrounding structures than most other 

 veins, and are less capable of resisting increased blood pressure: the condition is favored by 

 gravitation, being influenced by the erect posture, either sitting or standing, and by the fact 

 that the superior hsemorrhoidal and portal veins have no valves: the veins pass through mus- 

 cular tissue and are liable to be compressed by its contraction, especially during the act of 

 defecation : they are affected by every form of portal obstruction. 



