The radial artery, which is the smaller of the two divisions, pursues nearly the same direction ns the brachial, and in the lower part of the upper third of the fore-arm is found exactly midway between the radial and ulnar surfaces, overlapped by the supinator radii longus, and lying upon the tendon of the pronator radii teres muscle, with the radial nerve about a quarter of an inch to its outer side, arid separated by fat and cellular mem bmne. From this point the radial artery descends towards the wrist-joint, and at the lower part of the upper half of the fore-arm quits the pronator radii teres, and passes on to the anterior surface of the flexor longus pollicis, having the flexor carpi radialis to its inner side. A little lower down, that is, at the upper part of the lower third, the vessel emerges from beneath the supinator radii longus muscle, and is covered only by the fascia. In its further course to the wrist-joint the flexor carpi radialis maintains its position on the inner side, to which the tendon of the supinator radii longus corresponds on the outer. The radial nerve no longer accompanies the vessel, for it has now slid under the supinator radii longus, and reached the posterior face of the arm. As the radial artery just above the wrist-joint is covered only by the fascia, and lies upon the bone, its pulsations are easily felt, and in con sequence of its convenient situation is generally selected by the medical practitioner to ascertain the general state of the circulation. NVe should, however, always bear in mind the great variety both in size and distribution to which this vessel is liable, and take the precaution of at least examining the radial artery in both arms.
The inner edge of the supinator radii muscle is a certain guide to the situation of this artery should the surgeon be required to secure it, and this should always be effected by two ligatures, as its free anastomosis below will certainly produce secondary hemorrhage if this precaution is neglected. As the nerve lies on the outer side of the artery, the needle must be passed from without inwards.
The ulnar artery has a deep course, first passing beneath the median nerve, which se parates it from the pronator radii teres muscle, next beneath the flexor digitorum sublimis, the two last muscles separating it from tho flexor carpi radial's and palmaris longus, and upon the flexor digitorum profuudus, and when it reaches the tendon of this muscle midway between the wrist and elbow-joints, it comes into contact with the ulnar nerve, by which it is separated from time flexor carpi ulnaris muscle on its inner side. In its further descent to the wrist joint it is situated between the flexor communis digitorum sublimis and flexor carpi ulnaris. Gradually sliding behind, the tendon of the latter remains covered by it for about two inches above the annular liga ment of the wrist, in front of which it passes into the palm of the hand. The third branch
worthy of mention in this division of the fore arm is the anterior interosseal. This vessel is a branch of the ulnar artery, and not unfre quently is of large size, though usually of a calibre about intermediate to the two last men tioned. It arises from the ulnar artery where that vessel is covered by the pronator radii teres, and descending towards the interosseal ligament reaches that structure a little below the tendon of the biceps. It is accompanied by a branch of the median nerve in its course downwards ; lies between the interosseous liga ments and the external edge of the flexor com munis digitorum profundus ; it terminates by dividing into two branches, of which one passes backwards through the interosseal liga ment, anastomosing with the posterior inter osseal, and the other, a small branch, descends over the wrist-joint into the palm of the hand, where it anastomoses with the deep palmar arch.
In the posterior region of the fore-arm we meet with only one vessel of any size ; this is the posterior interosseal artery, a branch from the anterior interosseal, which passes through the interosseal ligament opposite the tubercle of the radius; its course is not so straight and uniform as the anterior, its distri buent branches are larger and more numerous, and it may be said to ramble down between the extensor muscles and the interosseal liga ment, though it does not lie so immediately in contact with the ligament as the anterior inter osseal. It terminates by anastomosis with the vessels about the wrist-joint.
Such is the usual distribution of these ves sels ; they are, nevertheless, subject to every kind of variety, and the operator previously to the commencement of an operation ought always carefully to examine the course of these vessels in order to detect any anormal arrangement either in relation to their size or distribution.
The arteries of the fore-arm are more ex posed to accidents from cutting instruments than most other vessels in the body ; and the usual plan of securing the vessel in these cases is to apply two ligatures on the wounded trunk, one above and the other below the orifice, the latter being required in consequence of the free anastomosis of the vessels in the hand.
But the fore-arm is occasionally wounded by sharp penetrating instruments, which passing deeply into the fleshy mass, the vessel which has been wounded is not immediately indicated, and the surgeon is consequently at a loss to discover which of the three main trunks requires the application of a ligature.
An examination through the wound would tend to aggravate the mischief, and besides, the search is often attended with difficulty, and often unsatisfactory.