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.