926 



HUMAN ANATOMY. 



obstruction of one or the other of the venous tributaries. The chief results are : 

 (i) Enlargement of the Hver itself, at first congestive, later from hyperplasia. 

 Diminution in the quantity of bile or alteration in its character may cause constipa- 

 tion and indigestion ; or escape of its coloring matter and its absorption by the 

 hepatic veins may giv^e rise to jaundice. (2) From congestion of the gastric and 

 intestinal mucosa (through the superior and inferior mesenteric, splenic, and gastric 

 tributaries) there may develop indigestion, flatulence, eructations, and vomiting, often 

 bloody ; serous exudation into the bowel — intestinal indigestion, and diarrhoea, some- 

 times with black stools from decomposed blood — or into the general peritoneal 

 cavity — ascites ; enlargement and tenderness of the spleen ; hemorrhoids (from the 

 ' communication between the middle and inferior hemorrhoidal veins — systemic — and 

 the superior hemorrhoidal vein — portal) ; varicosities in the lower extremities, possibly 

 from the same communication between the ca^'al and portal systems, but oftener from 

 the direct interference by an enlarged liver with the current in the inferior ca\'a. 



Septic inflammation of the liver may reach that organ through any of the portal 

 tributaries. It is not uncommonly the result of infection originating during a dysen- 

 teric attack. Cancer may also reach the liver by venous channels, usually by the 

 gastric or hemorrhoidal tributaries. 



As the number of extraperitoneal anastomoses between the branches of the 

 parietal vessels (lower intercostal, phrenic, lumbar, ilio-lumbar, epigastric and circum- 

 flex iliac) and branches of vessels that supply viscera without a complete peritoneal 

 covering (liver, kidneys, suprarenals, duodenum, pancreas, ascending and descending 

 colon) are of great importance in case of obstruction to the visceral arterial supply, 

 so the corresponding venous anastomoses are of equal or greater importance in 

 obstruction of the portal vein or of the inferior cava. The occasional connection 

 between a parumbilical vein and the external iliacs — through the epigastrics — may 

 also relieve portal obstruction. The above anastomoses explain the eflect of leeches 

 or wet cups or counter-irritation of the surface in congestions or inflammations of 

 the partly extraperitoneal viscera. (Woolsey.) 



Fig. 



DEVELOPMENT OF THE VEINS. 



The embryonic venous system may be regarded as consisting of three sets of vessels. 

 One of these becomes the pulmonary veins, another gives rise to the portal andumbihcal veins, 

 while the third is represented by what are termed the cardinal veins. It is to these last that 

 attention may first be directed. 



The Cardinal Veins. — The cardinal veins (Fig. 776) are two longitudinal stems which 

 extend the entire length of the body, one on either side of the median line, receiving throughout 



their course lateral somatic and visceral branches 

 in more or less perfect segmental succession. 

 From each vein a branch passes medially towards 

 the heart, and the portion of the longitudinal 

 vein anterior to this cross-branch is termed the 

 anterior cardinal or primitive jugular, while 

 that behind it is known as \\\q posterior cardinal. 

 The cross-branch, which is usually described as 

 formed by the union of the anterior and pos- 

 terior cardinals, is termed the dnct of Cuvier. 



The anterior cardinals take their origin 

 from veins which ramify over the surface of the 

 brain and receive at first both the ophthalmic and 

 facial veins. Tlie cerebral veins later condense 

 to form the superior and inferior longitudinal, 

 the straight, and the lateral sinuses, with the last 

 of which the ophthalmic veins unite, their intra- 

 cranial portions becoming the cavernous and 

 inferior petrosal sinuses. The facial veins, how- 

 ever, sever their connection with the cerebral 

 veins and unite with other superficial veins to 

 form the external jugular — a vessel which in 

 some manunalia reaches a high degree of devel- 

 opment, almost or entirely replacing the internal jugular, which represents the main stem 

 of the cardinal. In man the original condition, in which the external jugular is of subordinate 



Stgmental 



veins * 



— Anterior cardinal 



Venous sinus of heart 

 Duct of Cuvier 



Vitelline vein 

 Umbilical vein 

 Posterior cardinal 



Diagram showing pViniary symmetrical 

 arrangement of venous system. 



