THE VEINS.
The veins are the vessels which return the blood to the heart, after it has been circulated by the arteries through the different tissues of the body; they are much thinner in structure than the arteries, so that when emptied of their blood they become flattened and collapsed.
The veins of the trunk may be divided into, the superior vena cava, with its formative branches, and the inferior vena cava with its formative branches.
The superior vena cava is formed by the junction of the right and left vena innominata; it is a short trunk about three inches in length; it descends perpendicularly on the right side of the arch of the aorta, and terminates in the upper part of the right auricle of the heart. The right vena innominata receives the veins of the neck, which return the blood from the head as follows: The internal, external and anterior jugular veins—the external jugular vein being the one which is ordinarily open to let out the extravasated blood from the head—it will not be amiss to describe its course; it descends the neck in the direction of a line drawn from the angle of the lower jaw to the middle of the clavicle or collar bone, and terminates into the sub-clavian vein; it is variable in size, and replaced by two veins. The sub-clavian vein becomes the axillary vein near the arm-pit, and opens into the brachial veins down to the bend of the elbow, where it is divided into several branches which supply the fore-arm and the hand.
The inferior vena cava is formed by the union of the two common iliac veins; it ascends along the front of the vertebral column or back bone, and, passing through the fissure in the posterior border of the liver, terminates into the inferior part of the right auricle of the heart. Its branches are the lumbar veins, three or four in number, which collect the blood from the muscles and integuments of the loins and spinal veins; the renal veins, which return the blood from the kidneys, and the hepatic veins in the liver.
The common iliac veins, which, by their union form the inferior vena cava, are in turn formed by the union of the internal and external iliac veins; the external iliac vein passing into the thigh becomes the femoral vein, and is found in the same sheath with the femoral artery; further below it becomes the popliteal vein; about one inch and a half below Poupart’s ligament in the upper part of the thigh, the femoral vein receives the internal saphenous vein, which commences at the inner side of the foot and great toe; it ascends in front of the inner ankle and along the inner side of the leg; it then passes behind, and along the inner side of the thigh to the saphenous opening, where it pierces the sheath of the femoral vessels and terminates as above stated, in the femoral vein.
The above explanation of the circulatory blood vessels is given only for one side of the body—the right side. The other vessels branching off from the two great trunks, the aorta and the vena cava, on the left side are the same, with very slight modifications.