OF THE LOWER EXTREMITY. 673 



The vesico-prostatic plexus surrounds the neck and base of the bladder and 

 prostate gland. It communicates with the haemorrhoidal plexus behind, and 

 receives the dorsal vein of the penis, which enters the pelvis beneath the subpubic 

 ligament. This plexus is supported upon the sides of the bladder by a reflection 

 of the pelvic fascia. The veins composing it are very liable to become varicose, 

 and often contain hard, earthy concretions, called phlebolit/t*. 



Surgical Anatomy. This plexus is wounded in the lateral operation of lithotomy, and it is 

 through it that septic matter finds its way into the general circulation after this operation. 



The dorsal vein of the penis is a vessel of large size which returns the blood 

 from the body of that organ. At first it consists of two branches, which are 

 contained in the groove on the dorsum of the penis, and it receives veins from the 

 glans. the corpus spongiosum, and numerous superficial veins ; these unite near the 

 roit of the penis into a single trunk, which passes through the suspensory ligament 

 of the penis, pierces the triangular ligament beneath the pubic arch, and divides 

 into two branches, which enter the prostatic plexus. 



The vaginal plexus surrounds the mucous membrane, being especially developed 

 at the orifice of the vagina ; it communicates with the vesical plexus in front, and 

 with the hiernorrhoidal plexus behind. 



The uterine plexus is situated along the sides and superior angles of the uterus, 

 between the layers of the broad ligament, receiving large venous canals (the uterine 

 sinuses) from the substance of the uterus. The veins composing this plexus 

 anastomose frequently with each other and with the ovarian veins. They are not 

 tortuous like the arteries. 



The Common Iliac Veins are formed by the union of the external and internal 

 iliac veins in front of the sacro-iliac articulation : passing obliquely upward 

 toward the right side, they terminate upon the intervertebral substance between 

 the fourth and fifth lumbar vertebrae, where the veins of the two sides unite at an 

 acute angle to form the inferior vena cava. The right common iliac is shorter 

 than the left, nearly vertical in its direction, and ascends behind and then to the 

 outer side of its corresponding artery. The left common iliac, longer and more 

 oblique in its coarse, is at first situated on the inner side of the corresponding 

 artery, and then behind the right common iliac. Each common iliac receives the 

 ilio-lumbar, and sometimes the lateral sacral, veins. The left receives, in addition, 

 the middle sacral vein. Xo valves are found in these veins. 



The middle sacral veins accompany the corresponding artery along the front 

 of the sacrum, and terminate in the left common iliac vein ; occasionally in the 

 angle of junction of the two iliac veins. 



Peculiarities. The left common iliac vein, instead of joining with the right in its usual 

 position, occasionally ascends on the left side of the aorta as high as the kidney, where, after 

 receiving the left renal vein, it crosses over the aorta, and then joins with the right vein to form 

 the vena cava. In these cases the two common iliacs are connected by a small communicating 

 branch at the spot where they are usually united. 1 



The Inferior Vena Cava returns to the heart the blood from all the parts below 

 the Diaphragm. It is formed by the junction of the two common iliac veins on 

 the right side of the intervertebral substance between the fourth and fifth lumbar 

 vertebrae. It passes upward along the front of the spine on the right side of the 

 aorta, and. having reached the under surface of the liver, is contained in a groove 

 on its posterior surface. It then perforates the central tendon of the Diaphragm, 

 enters the pericardium, where it is covered by its serous layer, and terminates in 

 the lower and back part of the right auricle. At its termination in the auricle it 

 is provided with a valve, the Euxtaehian. which is of large size during foetal life. 



Eelations. In front, from below upward, with the mesentery, right spermatic 

 artery, transverse portion of the duodenum, the pancreas, portal vein, and the 



1 See two case? which have been described by Mr. Walsham in the St. Bartholomew's Hospital 

 Reports,\o\s. xvi. and xvii. 

 43 



