984 THE VASCULAR SYSTEM. 



through which they communicate with the lateral sacral veins and receive blood from the 

 interior of the sacral canal. They unite, above, into a single middle sacral vein, which 

 terminates in the left common iliac vein. 



Vena Hypogastrica. The hypogastric vein (Fig. 777) is a short trunk formed 

 by the union of tributaries which correspond to all the branches of the hypogastric 

 artery, with the exception of the umbilical and the ilio-lumbar branches. 



It commences at the upper border of the greater sciatic notch, and ascends to the 

 aperture of the pelvis minor ; there it unites with the external iliac vein to form the 

 common iliac vein. It lies immediately postero-medial to the hypogastric artery, 

 is crossed laterally by the obturator nerve, and is in relation medially, on the left 

 side with the pelvic colon, and on the right side with the lower part of the ileum. 



Tributaries. The tributaries, which are numerous, are conveniently divisible into 

 extra-pelvic and intra-pelvic groups. 



The extra-pelvic tributaries are all parietal, and include the obturator, internal 

 pudendal, inferior, and superior glutseal veins. 



Obturator Vein. This vein is formed by the union of tributaries which issue from 

 the hip-joint and from the muscles of the proximal and medial part of the thigh. It 

 enters the pelvis minor through the obturator canal, runs backwards, along the lateral 

 wall of the pelvis minor, lying medial to the pelvic fascia, immediately below the corre- 

 sponding artery, and, passing between the hypogastric artery on the lateral side and the 

 ureter on the medial side, it terminates in the hypogastric vein. 



Inferior Gluteal Veins (O.T. Sciatic). The vense comites of the inferior gluteal 

 artery commence in the subcutaneous tissues on the back of the thigh ; they ascend with 

 the artery, and pass into the buttock on the deep aspect of the glutseus maximus, where 

 they receive numerous tributaries from the surrounding muscles. Entering the pelvis, 

 through the greater sciatic foramen, they unite into a single vessel, which terminates in 

 the lower and anterior part of the hypogastric vein below the termination of the obturator 

 vein. 



Superior Gluteal Veins (O.T. Glutseal). The vense comites of the superior gluteal 

 artery are formed by tributaries which issue from the muscles of the buttock. They 

 accompany the artery through the greater sciatic foramen, and terminate in the hypogastric 

 vein ; they frequently unite together before reaching their termination. 



Internal Pudendal Veins. The venae comites of the internal pudendal artery commence 

 by tributaries which emerge from the pudendal plexus, which lies below and posterior to 

 the arcuate ligament of the pubis and constitutes the anterior part of the prostatic plexus. 

 They receive blood from the corpus cavernosum penis, or the corpus cavernosum clitoridis, 

 by the deep vein of the penis or clitoris. They follow the course of the internal 

 pudendal artery, and usually join together into a single vessel (the internal pudendal 

 vein) which terminates in the hypogastric vein. They receive as tributaries the veins 

 from the bulb, the perineal and inferior hsemorrhoidal veins, and veins from the muscles 

 of the buttock. 



The inferior hsemorrhoidal veins, which commence in the substance of the external 

 sphincter of the anus and in the walls of the anal canal, anastomose with the middle and 

 superior hsemorrhoidal veins, and consequently connect the lowest parts of the portal and 

 vena caval systems together. 



The intra-pelvic tributaries of the internal iliac vein are either (a) parietal or 

 (b) visceral; the former comprises the lateral sacral veins, the latter includes the 

 efferent vessels from the plexuses around the several pelvic viscera. 



(a) Parietal : Lateral sacral veins accompany the lateral sacral arteries, and 

 terminate on each side in the postero-medial wall of the corresponding hypogastric vein. 



(b) Visceral tributaries are derived from the rectum and from the plexuses associated 

 with the uterus, vagina, bladder, and prostate. They include the middle hsemorrhoidal, 

 the uterine, the vaginal, and the vesical veins. 



The middle hsemorrhoidal veins are very irregular; sometimes they cannot be 

 distinguished. When present they are formed by tributaries which commence in the 

 submucous tissue of the rectum, where they communicate with the 'superior and inferior 

 hsemorrhoidal veins in the hsemorrhoidal plexus ; they pass through the muscular coat, 

 and fuse together to form two middle hsemorrhoidal veins, right and left, each of which 

 runs laterally, beneath the peritoneum, on the upper surface of the levator ani, to 

 terminate in the corresponding hypogastric vein. In the male each middle hsemorrhoidal 

 vein receives tributaries from the seminal vesicle and ductus deferens of its own side. 



