706 THE VEINS. 



Bernard's opinion ; and there is every reason to believe that the system of 

 the vena ports and that of the vena cava do not communicate, in the adult, 

 otherwise than by the capillary network which is intermediate to the interlobular 

 and sublobular vessels. If any other means of communication exist, they must 

 be extremely small. 



(Ligature of the portal vein causes distension of all the abdominal vessels, 

 and a highly congested state of the abdominal viscera ; whilst the blood-pressure 

 quickly falls, and the animal dies. So distensible are the abdominal vessels, 

 that they can contain nearly all the blood in the body. The ventricular systole 

 may send a pulse down the valveless posterior vena cava, and cause a pulse in 

 the liver. That gland swells with each systole, and relaxes with each diastole of 

 the heart.) 



Constitumt vessels of the vena portm. — The three roots of this vein are the 

 anterior and posterior mesenteries and the splenic vein. 



The collateral affluents it receives on its course are principally two : the 

 right gastro-epiploic or gastro-omental veins and anterior gastric. 



We will make a rapid survey of all these vessels. 



1. Roots of the Vena Port^. 



A. Anterior Mesenteric or Anterior Mesaraic Vein (Figs. 380, 44 ; 

 390, 2, 7). — This is an enormous venous canal into which flows the blood that 

 has passed through the walls of the small intestine, caecum, large colon, and 

 the origin of the small colon, the divisions of which con-espond exactly to 

 the different branches furnished by the anterior mesenteric artery. 



When traced from its opening to its origin, in an inverse direction to the 

 course of the blood, it is observed to lie between the two colic arteries, and 

 proceed beyond the flexure formed by the supra-sternal and diaphragmatic 

 flexures, beyond which it divides into two satellite branches for the colic 

 arteries, which anastomose in arcade towards the pelvic flexure, like the arteries 

 they accompany. 



It is therefore by the union of two colic veins (Fig. .390, 8, 9) that the 

 anterior mesenteric vein is constituted, and in this formation numerous collateral 

 affluents concur ; among these may be noticed the two cceecd veins (Fig. 390, 

 5, 6), the ilio-ccecal vein (Fig. 390, 4) coming from the origin of the floating 

 colon, and the veins of the small intestine — vessels arranged so exactly like the 

 corresponding arteries, that we may dispense with any further description of 

 them. 



B. Posterior Mesenteric or Posterior Mesaraic Vein (Figs. 389, 43 ; 

 390, 12). — This vessel commences above the rectum, near the anus, by large 

 hcmiorrhoidal branches which communicate with the homonymous ramuscules 

 of the internal pudic. It is directed forwards, between the two layers of the 

 second mesentery, along the small mesenteric artery, which it passes, and extends 

 to the great mesenteric artery, on the left side of which it unites with the splenic 

 vein, before opening into the anterior mesenteric to form the vena portfe. In 

 its course it receives all the satellite venous branches of the divisions of the 

 artery of the same name, the arrangement of these being similar to that of the 

 arterial ramifications. 



C. Splenic Vein (Fig. 390, 13). — This is an enormous canal which 

 accompanies the splenic artery, and comports itself exactly like it. It begins 

 by the left gastro-omental vein (Fig. 390, 14) anastomosing in arcade with the 



