212 HUMAN ANATOMY. 



front and two behind. The anterior longitudinal spinal veins, 

 two in. number, extend along the sides of the vertebral bodies 

 and opposite the bodies communicate by transverse trunks, which, 

 in their passage beneath the vertebral ligament, receive the di- 

 ploic veins, or vence basis vertebrce, from the interior of the body. 

 The posterior longitudinal veins, also two in number, smaller 

 than the anterior, extend down the vertebral arches and are con- 

 nected by transverse branches opposite the latter. 



They receive the veins from the spinal cord and its mem- 

 branes. 



3. The vence basis vertebrce return the blood from the bodies 

 of the vertebras into the anterior intraspinal plexuses. 



The vence medulli spinalis are the essential veins of the cord, 

 situated between the arachnoid and pia mater. 



Common Iliac Veins. 



Formed by the internal and external iliac veins uniting 

 opposite the sacro-iliac articulation, pass beneath the right com- 

 mon iliac artery to a point a little to the left of the body of the 

 last lumbar vertebra, w r here they unite to form the inferior vena 

 cava. The right is shorter and more vertical in its course, and 

 both are without valves. 



THE INTERNAL ILIAC VEIN corresponds to the distribution 

 of the corresponding artery. 



It receives the following venaa comites : 



Gluteal, Internal pudie, 



Sciatic, Lateral sacral, and 



Obturator, Middle sacral; 



and the following plexuses : 



Vesico-prostatic, 1 . , Uterine and 



Hamiorrhoidal, / ir Vaginal, 



The lateral and middle sacral form a small plexus the 

 plexus sacralis. 



The veins of the rectum, bladder, and generative organs 

 anastomose freely and form three plexuses : 



1. Hcemorrlioidal plexus encircles the lower part of the rec- 

 tum, communicates with the sacral and prostatic plexuses, and 

 veins from it join the inferior mesenteric, internal iliac, and 

 pudic veins. 



2. V esico-prostatic plexus surrounds the membranous por- 

 tion of the urethra, neck of bladder, prostate body, and seminal 

 vesicles. It communicates behind with the hasmorrhoidal. 



