Such venous pumps are found in many places - in the thigh, popliteal space and lower leg, in the arm, forearm and hand, near the lower jaw, clavicle, etc.

The femoral vein is affected as above described throughout its whole length. In its lower part sartorius and a fibrous membrane from adductors longus and magnus to vastus internus lie over the vessel, which is widened when the membrane becomes tense on contraction of sartorius.

Higher up a fascia with a free upper border goes from sartorius at the saphenous opening to the pectineal fascia; here the falciform process is attached to Poupart's ligament. Beyond the saphenous opening the vein is therefore covered by a membrane which is lifted when sartorius contracts. Where the femoral vein enters the external iliac vein the vessel is covered by Poupart's ligament; the femoral vein is here connected by its funnel-shaped sheath (of Linhart) to Poupart's and Gimbernats ligaments. Both the upper part of the femoral vein and the lower part of the external iliac Vein therefore become widened when Pouparts ligament becomes tense, i.e., when the oblique muscles of the abdomen contract, or in outward rotation of the thigh or extension of the hip joint. In the same way one finds in these movements that the femoral vein below this area is emptied of blood. The same portion of the vein, on the other hand, becomes well filled with blood when the thigh is rotated inwards and flexed at the hip joint.

Just in the region where his arrangement acts the femoral vein receives a large supply of blood from different areas through the great saphenous, the external superficial, and deep pudic, the superficial epigastric, the superficial circumflex iliac, the deep inferior epigastric, the internal and external circumflex, deep femoral and pubic veins, and venae comites - a list which gives the reader some idea of the special influence of walking on the circulation of the lower extremities and adjoining regions.

In the popliteal space the mechanism is easily seen, the vein lying in the space which is bounded in front by the joint, at the sides by biceps, semi-membranosus, semi-tendinosus, and both heads of gastrocnemius, behind by fascia. This becomes tense on slight flexion of the knee joint, and by enlarging the space widens the vein, but on full flexion of the knee joint it becomes relaxed, so that the atmospheric pressure from without presses the fascia in towards the above-mentioned space and presses together the walls of the vein, which is thus filled and emptied by the same movement.

In the axilla the arrangement of fascia between pectoralis major on one side and latissimus dorsi and teres major on the other acts with the muscles in the way above described on the axillary vein, now filling, now emptying it; this helps the smaller tributary veins.

The axillary vein lies between pectoralis minor and the scaleni, in a space which by enlarging and diminishing has an effect on the circulation.

At the large venous angle in the lower part of the neck, into which both veins and the larger lymphatics open, sterno-cleido-niastoid, which is almost always more or less contracted, holds the jugular vein well open. The middle layer of cervical fascia, lying under the muscle, is attached below to the sternum and clavicle, and above to omohyoid. The contraction of omohyoid therefore also holds the jugular vein open. But when the shoulder is lowered and the head at the same time is turned towards the other shoulder, omohyoid has a compressing effect on the vein.

In the neck platysma lifts the skin over the veins, and thus has a widening effect on them.

In active as in passive movements the blood vessels are stretched, especially the veins, and thus increase their capacity, in spite of becoming at the same time rather compressed, so that the amount of blood in the stretched area is increased. When during movement in the opposite direction the vessels are again shortened, part of their contents is pressed on towards the heart. The powerful inferior vena cava especially undergoes very considerable alterations in its size during movements in the lumbar region. According to this law the pulmonary vessels contain more during inspiration, less again during expiration, and the respiratory movements in this way considerably assist pulmonary circulation.

There is reason to suppose that movements in the lumbar region, Trunk-rolling, Side-flexions, Trunk-forward-bendings, etc., have to some extent the power of compressing the abdominal organs, especially the liver and spleen, from which the blood is to some extent squeezed out like water out of a sponge, thus increasing the stream in the inferior vena cava.

Muscle work causes stronger heart-beats and increases their rate. To a small extent this is the result of the effect upon the venous flow already referred to, and increases the supply of blood to the heart. But it is chiefly on account of the presence in the blood of metabolic products, which arise during muscle action, and which stimulate both the heart muscle itself and the nerve centres which regulate cardiac activity. A reflex effect from the tissues thirsting for oxygen and nourishment was formerly thought to be the cause, but is now denied. During muscle action the heart dilates more strongly in diastole, contracts more forcibly in systole, with each beat forces a greater quantity of blood into the aorta, and performs this more times in a minute than while resting.

Respiration has a strong influence upon circulation, and he who wishes to demonstrate the physiological and therapeutic effects of physical exercise will do well to consider this influence in connection with the description of the circulation.

Physical exercise works strongly upon the circulation, in that it gives rise to substances in the blood which excite the respiratory centre in the floor of the fourth ventricle and in this way cause deeper and more frequent respirations.