554 VEINS. 



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 root of the penis into a single trunk, which 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 de- 

 veloped at the orifice of the vagina ; it communicates with the vesical plexus 

 in front, and with the haemorrhoidal plexus behind. 



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

 receiving large venous canals (the uterine sinuses) from its substance. 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- vertebral articulation ; passing obliquely up- 

 wards towards 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 course, is at first situated on the inner side of the cor- 

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

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

 ceives, in addition, the middle sacral vein. No valves are found in these veins. 



The middle sacral vein accompanies its corresponding artery along the front 

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

 the commencement of the inferior vena cava. 



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

 tion, 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. Jn these cases, the two common iliacs are connected by a small communicating branch 

 at the spot where they are usually united. 



The Inferior V-ena 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 upwards 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 in its posterior border. It then perforates the tendinous centre 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 Eustachian, which is of large size 

 during fcetal life. 



.Relations. In front, from below upwards, with the mesentery, transverse 

 portion of the duodenum, the pancreas, portal vein, and the posterior border of 

 the liver, which partly and occasionally completely surrounds it ; behind, with 

 the vertebral column, the right cms of the Diaphragm, the right renal and 

 lumbar arteries; on the left side, with the aorta. It receives in its course the 

 following branches: 



Lumbar. Suprarenal. 



Right spermatic. Phrenic. 



Renal. Hepatic. 



Peculiarities. In Position. This vessel i* sometimes placed on the left side of the aorta, as 

 high as the left renal vein, after receiving which, it crosses over to its usual position on the 

 right side; or it may be placed altogether on the left side of the aorta, as far upwards as i's 

 termination in the heart: in such cases, the abdominal and thoracic viscera, together with the 

 great vessels, are all transposed. 



