VEINS OF THE PELVIS. 517 



The middle sacral artery of the aorta (p. 489), (fig. 176, b) descends 

 along the middle of the last lumbar vertebra, the sacrum, and the coccyx. 

 The artery gives small branches laterally, opposite each piece of the 

 sacrum, to anastomose with the lateral sacral arteries, and to supply the 

 nerves, and the bones with the periosteum. Sometimes a small branch is 

 furnished by it to the lower end of the rectum, to take the place of the 

 middle haemorrhoidal artery. 



The INTERNAL ILIAC VEIN receives the blood from the wall of the pel- 

 vis, and the pelvic viscera, by branches corresponding for the most part 

 with those of the arteries. The vein is a short thick trunk, which is 

 situate at first on the inner side of the internal iliac artery; but as it 

 ascends to join the external iliac, it passes behind, and to the outer aspect 

 of its companion artery on the right side 



Branches. Most of the branches entering the trunk of the internal 

 iliac vein, have the same anatomy as the arteries; but the following vis- 

 ceral branches the pudic and dorsal of the penis, the vesical and haemor- 

 rhoidal, the uterine and vaginal, have some peculiarities. 



The pudic vein receives roots corresponding with the branches of the 

 pudic artery in the perin,T.um, but not those corresponding with the offsets 

 of the artery on the dorsum of the penis. 



The dorsal vein of the penis receives veins from the corpora cavernosa 

 and corpus spongiosum of the penis, and piercing the triangular ligament 

 of the urethra, divides into two, a right and a left branch, which enter a 

 plexus around the prostate. 



The superior hcemorrhoidal vein commences in a large plexus (ha^mor- 

 rhoidal) around the lower end of the rectum beneath the mucous mem- 

 brane (p. 533). 



The vesical veins begin in a plexus about the lower part of the bladder, 

 and anstomose with the prostatic and hremorrhoidal veins. 



The uterine veins are numerous, and form a plexus in and by the side 

 of the uterus : this plexus inosculates above with the ovarian plexus, and 

 below with one on the vagina. 



Tne vaginal veins surround their tube with a large vascular plexus. 



Parietal veins of the pelvis. Three veins of the wall of the pelvis, viz., 

 ilio-lumbar, lateral sacral, and middle sacral, open into the common iliac 

 vein. 



Dissection (fig. 177). To dissect the nerves of the pelvis, on the right 

 side, ' it will be necessary to detach the triangular ligament with the 

 urethra from the arch of the pubes ; and to cut through, on the right side, 

 the recto- vesical fascia and the levator ani, together with the visceral arte- 

 ries, in order that the viscera may be drawn somewhat from the side of 

 the pelvis. If the bladder is distended let the air escape from it. 



By means of the foregoing dissection the sacral nerves may be found as 

 they issue from the sacral foramina. The dissector should follow the first 

 four into the sacral plexus, and some branches from the fourth to the vis- 

 cera. The last sacral and the coccygeal nerve are of small size, and will 

 be detected coming through the coccygeus muscle, close to the coccyx ; 

 these are to be dissected with care-; and the student will succeed best by 

 tracing the connecting filaments which pass from one to another, beginning 

 above with the offset from the fourth nerve. 



Opposite the lower part of the rectum, bladder, and vagina is a large 

 plexus of the sympathetic (pelvic plexus), which sends branches to the 

 viscera along the arteries. This plexus is generally destroyed in the pre- 



