PORTAL SYSTEM. 349 



tercostals ; and in the loins and pelvis into the lumbar and sacral veins, 

 the communications being established through the intervertebral foramina. 

 The Medulli-spinal veins are situated between the pia mater and arach- 

 noid ; they communicate freely with each other to form plexuses, and they 

 send branches through the intervertebral foramina with each of the spinal 

 nerves, to join the veins of the trunk. 



CAREIAC VEINS. 



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



Great cardiac vein, 

 Posterior cardiac veins, 

 AnteriorVardiac veins, 

 Venae 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 ven- 

 tricles; it then curves around the left auric ulo-ventricular groove to the 

 posterior part of the heart, where it terminates in the right auricle. It re- 

 ceives 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 ventricular groove, 

 to terminate in the great cardiac vein. It receives the veins from the pos- 

 terior aspect of the two ventricles. 



The Anterior cardiac veins collect the blood from the anterior surface 

 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 terminate in the great cardiac vein 

 near its entrance into the right auricle. 



The Vena 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 haernorrhoidal veins, and from the sigmoid flexure and de 

 scending colon, and ascends behind the transverse duodenum and pan 

 creas, to terminate in the splenic vein. Its haBmorrhoidal branches inos 

 culate with branches of the internal iliac vein, and thus establish a com 

 munication between the portal and general venous system. 



The Superior mesenteric vein is formed by branches which collect the 

 venous blood from the capillaries of the superior mesenteric artery; they 

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