#Subcutaneous rupture# of veins occur most frequently in association with fractures and in the reduction of dislocations.  The veins most commonly ruptured are the popliteal, the axillary, the femoral, and the subclavian.  On account of the smaller amount of elastic and muscular tissue in the wall of a vein, the contraction and retraction of its walls are less than in an artery, and so bleeding may continue for a longer period.  On the other hand, owing to the lower blood-pressure the outflow goes on more slowly, and the gradually increasing pressure produced by the extravasated blood is usually sufficient to arrest the haemorrhage before it becomes serious.  As an aid in diagnosing the source of the bleeding, it should be remembered that the rupture of a vein does not affect the pulsation in the limb beyond.  The risks are practically the same as when an artery is ruptured, excepting that of aneurysm, and the treatment is carried out on the same lines, but it is seldom necessary to operate for the purpose of applying a ligature to the injured vein.

#Wounds# of veins—­punctured and incised—­frequently occur in the course of operations; for example, in the removal of tumours or diseased glands from the neck, the axilla, or the groin.  They are also met with as a result of accidental stabs and of suicidal or homicidal injuries.  The haemorrhage from a large vein so damaged is usually profuse, but it is more readily controlled by external pressure than that from an artery.  When a vein is merely punctured, the bleeding may be arrested by pressure with a pad of gauze, or by a lateral ligature—­that is, picking up the margins of the rent in the wall and securing them with a ligature without occluding the lumen.  In the large veins, such as the internal jugular, the femoral, or the axillary, it is usually possible to suture the opening in the wall.  This does not necessarily result in thrombosis in the vessel, or in obliteration of its lumen.

When an artery and vein are simultaneously wounded, the features peculiar to each are present in greater or less degree.  In the limbs gangrene may ensue, especially if the wound is infected.  Punctured and gun-shot wounds implicating both artery and vein are liable to be followed by the development of arterio-venous aneurysm.

#Entrance of Air into Veins—­Air Embolism.#—­This serious, though fortunately rare, accident is apt to occur in the course of operations in the region of the thorax, neck, or axilla, if a large vein is opened and fails to collapse on account of the rigidity of its walls, its incorporation in a dense fascia, or from traction being made upon it.  If the wound in a vein is thus held open, the negative pressure during inspiration sucks air into the right side of the heart.  This is accompanied by a hissing or gurgling sound, and with the next expiration some frothy blood escapes from the wound.  The patient instantly becomes pale, the pupils dilate, respiration becomes laboured, and although the heart may continue to beat forcibly, the peripheral pulse is weak, and may even be imperceptible.  On auscultating the heart, a churning sound may be heard.  Death may result in a few minutes; or the heart may slowly regain its power and recovery take place.