The umbilical vein originates by means of capillaries in the placenta, traverses the cord and enters the body of the child at the umbilicus. The umbilical vein now enters the substance of the liver and passes from that organ to the ascending vena cava by means of the ductus venosus. The blood now enters the right auricle of the heart and the eustachian valve is so placed that this blood is thrown directly into the left auricle of the heart, from there into the left ventricle, and out into the aorta to find itself in the general circulation of the child. The blood coming from the upper extremities of the child finds its way into the right auricle of the heart by means of the descending vena cava, thence into the right ventricle, and out into the pulmonary artery. This artery after birth will lead the blood to the lungs, but before birth, in as much as the lungs are not functioning, the lungs can not accommodate this amount of blood, so it passes directly into the arch of the aorta by means of the ductus arteriosus, and thence into the general circulation. The umbilical or hypogastric arteries leave the internal iliacs, pass one on each side of the bladder to the umbilicus, and thence down the cord to the placenta, end there in capillaries, where the blood is now purified, and nourished for its return flow. =The Collateral Circulation.=—By collateral circulation is meant the anastomoses of arteries, or veins through a side branch. There are three great arterial collateral circulations in the body. One is in the arm, the deep brachial artery, and the anastomotica magna, coming off of the brachial artery and anastomosing with the recurrent radial and ulnar artery. One is in the leg, the deep femoral artery, and the anastomotica magna coming off of the femoral artery and anastomosing with the recurrent anterior and posterior tibial arteries. One over the front part of the body, the superior and inferior mammary arteries branches of the subclavian artery and anastomosing with the superior and inferior epigastric arteries, branches of the external iliac and femoral arteries. [Illustration: FIG. 45—Collateral anastomosis of veins (Poirier and Charpy)] =The Lymphatic Circulation.=—The lymphatic system is a system of vessels which occurs abundantly in almost all portions of the body and converge and anastomose to form two or more main trunks, which open into the subclavian veins just before they are joined by the internal jugular. The vessels contain a fluid termed lymph, usually colorless and containing numerous white blood corpuscles known as lymphocytes.