THE INFERIOR CAVAL SYSTEM. 909 



between the prostate gland and the bladder and is termed the vesico-prostatic plexus. 

 In the female the plexus lies at the sides and base of the bladder, and from its 

 relations posteriorly is known as the vesico-vaginal plexus. From their origin 

 the vesical veins pass upward, outward, and backward to open into the internal 

 iliac. 



The vesico-prostatic or vesico-vaginal plexus (plexus vesicalis), occupying 

 the position indicated above, is formed principally by the veins which drain 

 the urinary bladder and, in the male, the prostate gland. Posteriorly, in the 

 male, the plexus communicates with the external hemorrhoidal plexus, and in the 

 female with the vaginal plexus, and anteriorly, in both sexes, it communicates 

 extensively with the pudendal plexus. In addition to the drainage which it 

 possesses through the vesical veins, it also drains by way of the obturator veins, 

 branches from it joining those vessels just after they have passed through the 

 obturator foramina. 



The pudendal plexus (plexus pudendalis), also known as the plexus of Santo - 

 rini, occupies the space between the lower part of the pelvic surface of the symphysis 

 pubis and the anterior surface of the neck of the bladder, becoming continuous 

 posteriorly at the sides with the vesico-prostatic (vesico-vaginal) plexus. Its chief 

 tributary is the deep dorsal vein of the penis (clitoris) (v. dorsalis penis vel 

 clitoridis), which is a single large vein (sometimes partly double in the female) which 

 passes along the dorsal mid-line of the penis or clitoris, beneath the deep fascia 

 (Fig. 767), in the groove between the two corpora cavernosa, and has on either side 

 of it one of the two dorsal arteries. It receives branches from the corpora cavernosa 

 and has its origin in two veins which curve from below upward around the base of 

 the glans penis (clitoridis). At the root of the penis (clitoris) it leaves the dorsal 

 surface and perforates the triangular ligament of the perineum, usually just below the 

 border of the subpubic ligament, so entering the pelvis. It then bifurcates, each of 

 the branches passing into the pudendal plexus. Before entering the pelvis it gives 

 off on either side a small branch which unites with the internal pudic vein, thus 

 representing the course of the artery. 



In addition to the dorsal vein of the penis (clitoris), the pudendal plexus also 

 receives branches from the internal pudic vein and from the anterior surfaces of the 

 bladder and, in the male, the prostate. It communicates posteriorly and at the 

 sides with the vesico-prostatic (vesico-vaginal) plexus, and through it finds its chief 

 efferents in the vesical veins, although it is also drained by the obturator veins, with 

 each of which it communicates by one or two branches. 



The External Iliac Vein. 



The external iliac vein (v. iliaca externa) (Figs. 766, 767) begins at Poupart's 

 ligament, where the femoral vein becomes continuous with it, and passes upward, 

 backward, and inward to the level of the sacro-iliac articuladon, where it unites with 

 the internal iliac to form the common iliac. 



Its course is along the line of junction of the false and the true pelvis, and it lies 

 upon the inner border of the psoas muscle and internal, or in its upper part internal 

 and posterior, to the external iliac artery. Near its termination it is crossed by the 

 internal iliac artery, on the left side almost at a right angle, on the right more 

 obliquely. Valves are present in about 35 veins out of 100, but in a third of 

 such cases they are insufficient. 



Tributaries. ^The tributaries of the external iliac vein are : (i) the deep epi- 

 gastric and (2) the deep circumflex iliac veins. 



I. The Deep Epigastric Vein. — The deep epigastric vein (v. epigastrica 

 inferior) has its origin above the umbilicus in the substance of the rectus abdominis 

 muscle, where it anastomoses with the superior epigastric vein. It accompanies the 

 deep epigastric artery as two venae comites which unite below to form a single trunk 

 opening into the external iliac a short distance above Poupart's ligament. 



Below the level of the umbilicus the vein is provided with valves whose concav- 

 ities are directed downward, but above the umbilicus it is said to be destitute of 

 valves. It receives tributaries from the rectus muscle and, as it passes beneath the 



