When an artery of one of the extremities has been injured in any of the above ways, the blood is effused into the surrounding cellular tissue, forming an extravasation, if unable to escape from the outer wound. The blood is then accumulated in a cavity formed by the laceration of the tissue, the structures around it being suffused and infiltrated with blood. This constitutes diffuse false aneurism, or, according to Foubert, primary false aneurism. When considerably diffused it in general terminates fatally in inflammation degenerating into gangrenous disintegration, associated with symptoms of paralysis, and in continuous external hemorrhage. It is only in rarer cases, and when the aneurism is less diffused, that it can heal by the artery becoming obliterated during the ichorous process, through arteritis, and by the drying up of the ulcerous process, after expulsion of the extravasation and of the tissue destroyed by it.

When the neighborhood of the extravasation becomes the seat of an inflammatory process (reaction), tending to condensation (sclerosis) and hypertrophy of the tissue, the cavity containing the extravasation acquires a true wall and definite limits, and becomes converted into a sac, seated upon and surrounding the artery, and into which the arterial wound opens. A lining membrane may be formed upon its inner surface, and the sac may then present such similarity with a mixed aneurism as to render its anatomical diagnosis extremely difficult. In this condition, the collective appearances represent what is commonly known as false circumscribed, or Foubert's consecutive false aneurism.

It is obvious that these conditions do not originally merit the designation of aneurism, whilst the consecutive condition of a false circumscribed aneurism presents appearances which give it in every respect the significance of an aneurism. This form of aneurism, which commonly attains a very large size, as, for instance, in the popliteal space generally, as is the case with large aneurisms, terminates fatally when left to run its course.

On varicose aneurism, Aneurysma spurium varicosum, Varix aneu-rysmaticus, A. per anastomosin (W. Hunter), A. per transfusionem (Dupuytren).

This aneurism consists in the communication of an artery with a neighboring vein, effected by means of an aperture in the artery corresponding to one in the vein. This communication may be direct or indirect, and further may be the result of injury, or may occur spontaneously.

Varicose aneurism is most commonly produced by some injury which simultaneously affects the contiguous walls of an artery and of a vein; such, especially, as penetrating wounds or injuries from small shot, and when it arises from incised wounds, it is in general owing to venesection in which both walls of the vein have been cut through, and the lancet has penetrated through the wall of the artery below it. The latter mode of injury is, moreover the most frequent cause of varicose aneurism, and consequently the bend of the elbow is the most common seat of this aneurismal formation. Moreover, neighboring arteries and veins may be so much injured by splinters of bone that the arterial blood may enter a vein. The same result has also been effected by violent contusions.

The most common form of traumatic varicose aneurism is that occurring after venesection, and seated between the brachial artery and the median vein, or when the brachial artery divides higher up, between the radial or ulnar artery and the median, cephalic, or basilic vein. The same form of aneurism has also been observed in the brachial artery in the upper arm, in the subclavian, in the carotid with the jugular vein, in the femoral, popliteal, temporal, and other arteries.