=The Coronary Circulation.=—The heart receives its blood supply through the two coronary arteries which arise from the aorta immediately above its origin, the return flow being by the coronary veins which open into the right auricle of the heart by the coronary sinus. The branches of the coronary arteries upon the surface of the heart are, as a rule, all end arteries; that is, arteries which form no direct anastomosis with their neighbors. Practically no blood can be carried directly, therefore, by the left coronary artery into the territory supplied by the right one, or vice versa. The coronary sinus is a short venous trunk a little over an inch in length, which occupies the right half of that portion of the auriclo-ventricular groove which lies between the left auricle and ventricle. At the right end it opens into the right auricle, its orifice being guarded by the Thebesian valve. [Illustration: FIG. 42—A front view of the heart showing coronary arteries. (Spalteholz)] [Illustration: FIG. 43—A back view of the heart showing the coronary sinus, and vessels entering and leaving. (Spalteholz)] =The Portal Circulation.=—This circulation is of little or no value to the embalmer, as no part of it is directly required to supply any of the tissues with embalming fluid. The portal circulation is formed by the superior mesenteric vein and the splenic vein uniting to form the portal vein. The inferior mesenteric vein runs into the splenic vein; the gastric and cystic veins run into the portal veins. The portal vein ends in capillaries in the liver, where certain important changes take place, namely, the taking out of the bile. The portal vein and its tributaries are unlike the veins in the general circulation, as there are no valves. Their function in life is to gather up food or nutrition for the blood, and to the embalmer is of no special importance, only to know how this circulation is made up. The vessels that convey blood to the liver in life and the fluid in death are discussed under the liver. After death, about one-fourth of the blood of the body is to be found in the portal system. This blood can in no way be removed, and this is one of the reasons why the embalmer is not able to draw more blood than he does. =The Foetal Circulation.=—The foetal circulation is that circulation existing between mother and unborn child.