344 PORTAL SYSTEM. 



the neck, into the intercostal veins in the thorax, and into the lumbar 

 and sacral veins in the loins and pelvis, by means of communicating 

 trunks, which escape at the intervertebral foramina. 



The Medutti-spinal veins are situated between the pia mater and 

 arachnoid ; they communicate freely with each other, and form 

 plexuses, and send branches through the intervertebral foramina with 

 each of the spinal nerves, to join the veins of the trunk. 



CARDIAC VEINS. 



The veins returning the blood from the substance of the heart, 

 are the 



Great cardiac vein, 

 Posterior cardiac veins, 

 . Anterior cardiac veins, 

 Vense Thebesii. 



The Great cardiac vein (coronary) commences at the apex of the 

 heart, and ascends along the anterior ventricular groove to the base 

 of the ventricles ; it then curves around the left auriculo- ventricular 

 groove to the posterior part of the heart, where it terminates in the 

 right auricle. It receives in its course the left cardiac veins from 

 the left auricle and ventricle, and the posterior cardiac veins from 

 the posterior ventricular groove. 



The Posterior cardiac vein, frequently two in number, commences 

 also at the apex of the heart, and ascends along the posterior ven- 

 tricular groove, to teminate in the great cardiac vein. It receives 

 the veins from the posterior aspect of the two ventricles. 



The Anterior cardiac veins collect the blood from the anterior sur- 

 face of the right ventricle ; one larger than the rest runs along the 

 right border of the heart and joins the trunk formed by these veins, 

 which curves around the right auriculo-ventricular groove, to termi- 

 nate in the great cardiac vein near to its entrance into the right 

 auricle. 



The VencB, Thebesii are numerous minute venules which convey 

 the venous blood directly from the substance of the heart into its 

 four cavities. Their existence is denied by some anatomists. 



PORTAL SYSTEM. 



The portal system is composed of four large veins which return 

 the blood from the chylopoietic viscera ; they are the 



Inferior mesenteric vein, 

 Superior mesenteric vein, 

 Splenic vein, 

 Gastric veins. 



The Inferior mesenteric vein receives its blood from the rectum by 

 means of the hamorrhoidal veins, and from the sigmoid flexure and 

 descending colon, and ascends beneath the transverse duodenum and 



