A knowledge of the arteries of the forearm is necessary on account of the troublesome hemorrhage which they cause when wounded.

At the bend of the elbow, a finger's breadth below the crease and opposite the neck of the radius, the brachial artery divides into the radial and ulnar arteries. These are continued through the forearm to enter the hand, the ulnar anteriorly over the annular ligament and the radial posteriorly through the "anatomical snuff-box".

The ulnar artery is larger than the radial and in its upper half it describes a curve with its convexity toward the ulnar side passing beneath the pronator radii teres and superficial flexor muscles arising from the medial (internal) condyle. It is accompanied by venae comites but not by any nerve in this portion of its course. Just above the middle of the forearm the ulnar nerve joins the artery, lying to its ulnar side, and accompanies it down into the hand. In the lower half of its course the ulnar artery lies to the radial side of the flexor carpi ulnaris muscle, being slightly overlapped by it. The flexor sublimis on the radial side also tends to overlap it. The covering of the artery, partially at least, by these muscles, together with the thickness of the deep fascia and the lack of a proper bony support beneath, cause the pulse from the ulnar artery to be less distinctly felt than that from the radial. When the artery passes beneath the pronator radii teres muscle it is crossed by the median nerve, which lies superficial to the artery, and is separated from it by the deep head of the muscle. The branches of the ulnar artery in the forearm are the anterior and posterior ulnar recurrents, the common interosseous, muscular, nutrient, and anterior and posterior ulnar carpal branches (Fig. 329).

The anterior ulnar recurrent runs upward between the edges of the pronator radii teres and brachialis anticus.

Fig. 329.   Arteries of the forearm.

Fig. 329. - Arteries of the forearm.

The posterior ulnar recurrent passes upward with the ulnar nerve behind the medial (internal) condyle.

The common interosseous artery comes off from the ulnar about 2 to 3 cm. from its origin and divides into the volar (anterior) and dorsal (posterior) interosseous arteries. The anterior gives a branch to the median nerve - the comes nervi mediani - a nutrient branch to the radius, and, on reaching the upper edge of the pronator quadratus, sends a posterior terminal branch through the membrane and an anterior terminal branch into the muscle. The posterior interosseous passes beneath the oblique ligament to the back of the forearm and gives off the interosseous recurrent, which runs up between the lateral (external) condyle and the olecranon and then gives branches to the various muscles.

The radial artery, though smaller than the ulnar, seems to be a direct continuation of the brachial because it proceeds in the same general direction while the ulnar branches off to one side. It is divided into three parts according to the region it traverses, viz., the forearm, the wrist, and the hand. It describes a slightly outward curved line from a finger's breadth below the middle of the crease of the elbow to a point on the front of the radius at the wrist, 1 cm. (2/5 in.) inside of its styloid process. It is superficial in nearly its entire extent, being overlapped only by the edge of the brachioradialis (supinator longus) in its upper third. This muscle lies to its outer side all the way down to the styloid process. In the middle third the cutaneous branch of the radial nerve lies close to the outer side of the artery, but in the lower third the nerve leaves it to become subcutaneous, passing more toward the dorsum.

To the inner side of the artery is the pronator radii teres muscle in its upper third and the flexor carpi radialis for the rest of its course. At the wrist it rests on the anterior surface of the radius, a centimetre to the inner side of its styloid process. By compressing the vessel against the bone its pulsations can be readily felt, and here is where the finger is applied in taking the pulse.

. The branches of the radial artery are the recurrent, muscular, anterior radial carpal and superficial volar.

The radial recurrent arises from the radial soon after its origin and follows the radial nerve, in the groove between the brachialis anticus and brachioradialis.

The anterior carpal is a small branch which joins with the corresponding branch of the ulnar and anterior terminal branch of the anterior interosseous to form a so-called anterior carpal arch which anastomoses with branches of the deep palmar arch to supply the bones and joints of the carpus.

The superficial volar leaves the radial artery just before it crosses the external lateral ligament. It pierces the muscles of the thumb to anastomose with a superficial branch of the superficial palmar arch. Sometimes this artery is so large that it can be seen pulsating as it passes over the thenar eminence from the wrist downward.