LEPUS CUNICULUS 311 



The hepatic portal system consists of a series of veins 

 coming from all parts of the alimentary canal which ultimately 

 unite to form a large vessel, the hepatic portal vein, which, passing 

 forward in the mesentery near the post-caval vein, divides into 

 branches going to the various lobes of the liver. Its various factors 

 can readily be made out in a freshly killed animal when they are 

 usually full of blood. Four main trunks can be readily distinguished. 

 The posterior mesenteric vein comes from the hinder portion of the 

 rectum, and lies mainly in the mesorectum. The anterior mesenteric 

 vein is a larger trunk formed by the union of numerous vessels 

 coming from the front part of the rectum, the ilium, the coccum 

 and the colon. The duodenal loop and the pancreas are drained 

 by a single vessel, the duodenal vein, and the blood from the stomach 

 and spleen is returned by a lieno-gastric vein. 



Three main systemic or caval veins are present, two 

 anterior and one posterior. The right pre-caval vein (vena cava 

 anterior dextra) is formed by the junction of the jugular and sub- 

 clavian veins just in front of the first rib. It runs back on the 

 inner side of the right lung, and opens into the dorsal wall of the 

 right atrium. The azygos vein (azygos cardinal) is a small vessel 

 running forward along the right side of the vertebral column from 

 the posterior end of the thorax, receiving, as it does so, factors from 

 the hinder intercostal spaces. Finally it passes round the oesophagus 

 to open into the pre-caval, just before this enters the atrium. In 

 spite of its small size it is of interest, since it represents the persistent 

 remnant of the right posterior cardinal vein of the lower vertebrates 

 such as the dogfish, while all trace of it has disappeared in the frog. 

 The anterior phrenic vein is a small vessel bringing blood from the 

 ventral portion of the diaphragm, and opening into the ventral 

 side of the pre-caval. The right anterior intercostal vein is a short 

 dorsally situated vessel receiving factors from the anterior four or 

 five intercostal spaces and opening close to the preceding vein. 

 The right anterior epigastric vein (internal mammary) lies on the 

 ventral thoracic wall in close proximity to the corresponding artery, 

 and it joins the caval vein at the level of the first rib. 



The right sub-clavian vein is a stout trunk which drains the 

 right fore limbs and shoulder girdle, being termed the brachial vein, 

 in the upper arm. 



The right external jugular is a large vein running fairly super- 

 ficially the whole length of the neck, from just behind the angle 

 of the jaw where it is formed by the confluence of the anterior and 

 posterior facial veins, to the point where it joins the sub-clavian. 

 It drains the whole of the facial region and receives factors from the 

 oesophagus, trachea and various tissues of the neck. It has 



