A Treatise on Domestic Economy; For the Use of Young Ladies at Home and at School

vessels, the blood which is in them passes into as minute veins; and these run into each other, like the rills and branches of a river, until they are all united in two great veins, which run into the heart. One of these large receivers, called the _vena cava superior_, or _upper vena cava_, brings back the blood from the arms and head, the other, the _vena cava inferior_, or _lower vena cava_, brings back the blood from the body and lower limbs. In the preceding figure, H, is the heart, which is divided into four compartments; two, called _auricles_, used for receiving the blood, and two, called _ventricles_, used for sending out the blood. A, is the _aorta_, or great artery, which sends its branches to every part of the body. In the upper part, at _a_, _a_, _a_, are the main branches of the _aorta_, which go to the head and arms. Below, at _a_, _a_, are the branches which go to the lower limbs. The branches which set off at X, X, are those by which the intestines are supplied by vessels from the _aorta_. Every muscle in the whole body, all the organs of the body, and the skin, are supplied by branches sent off from this great _artery_. When the blood is thus dispersed through any organ, in minute vessels, it is received, at their terminations, by numerous minute veins, which gradually unite, forming larger branches, till they all meet in either the upper or lower _vena cava_, which returns the blood to the heart. V I, is the _vena cava inferior_, which receives the blood from the veins of the lower parts of the body, as seen at v, v. The blood, sent into the lower limbs from the _aorta_, is received by minute veins, which finally unite at v, v, and thus it is emptied through the lower _vena cava_ into the heart: _o_, _o_, represent the points of entrance of those tributaries of the _vena cava_, which receive that blood from the intestines, which is sent out by the _aorta_ at X,