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4b. 2. The Brachial Artery
FIG. 525 - The brachial artery. (A. Brachialis)
The brachial artery (Fig. 525) commences at the lower margin of the tendon of the Teres major, and, passing down the arm, ends about 1 cm. below the bend of the elbow, where it divides into the radial and ulnar arteries. At first the brachial artery lies medial to the humerus; but as it runs down the arm it gradually gets in front of the bone, and at the bend of the elbow it lies midway between its two epicondyles.Relations.—The artery is superficial throughout its entire extent, being covered, in front, by the integument and the superficial and deep fasciæ; the lacertus fibrosus (bicipital fascia) lies in front of it opposite the elbow and separates it from the vena mediana cubiti; the median nerve crosses from its lateral to its medial side opposite the insertion of the Coracobrachialis. Behind, it is separated from the long head of the Triceps brachii by the radial nerve and a. profunda brachii. It then lies upon the medial head of the Triceps brachii, next upon the insertion of the Coracobrachialis, and lastly on the Brachialis. Laterally, it is in relation above with the median nerve and the Coracobrachialis, below with the Biceps brachii, the two muscles overlapping the artery to a considerable extent. Medially, its upper half is in relation with the medial antibrachial cutaneous and ulnar nerves, its lower half with the median nerve. The basilic vein lies on its medial side, but is separated from it in the lower part of the arm by the deep fascia. The artery is accompanied by two venæ comitantes, which lie in close contact with it, and are connected together at intervals by short transverse branches. The Anticubital Fossa.—At the bend of the elbow the brachial artery sinks deeply into a triangular interval, the anticubital fossa. The base of the triangle is directed upward, and is represented by a line connecting the two epicondyles of the humerus; the sides are formed by the medial edge of the Brachioradialis and the lateral margin of the Pronator teres; the floor is formed by the Brachialis and Supinator. This space contains the brachial artery, with its accompanying veins; the radial and ulnar arteries; the median and radial nerves; and the tendon of the Biceps brachii. The brachial artery occupies the middle of the space, and divides opposite the neck of the radius into the radial and ulnar arteries; it is covered, in front, by the integument, the superficial fascia, and the vena mediana cubiti, the last being separated from the artery by the lacertus fibrosus. Behind it is the Brachialis which separates it from the elbow-joint. The median nerve lies close to the medial side of the artery, above, but is separated from it below by the ulnar head of the Pronator teres. The tendon of the Biceps brachii lies to the lateral side of the artery; the radial nerve is situated upon the Supinator, and concealed by the Brachioradialis. Peculiarities of the Brachial Artery as Regards its Course.—The brachial artery, accompanied by the median nerve, may leave the medial border of the Biceps brachii, and descend toward the medial epicondyle of the humerus; in such cases it usually passes behind the supracondylar process of the humerus, from which a fibrous arch is in most cases thrown over the artery; it then runs beneath or through the substance of the Pronator teres, to the bend of the elbow. This variation bears considerable analogy with the normal condition of the artery in some of the carnivora; it has been referred to in the description of the humerus (p. 212). As Regards its Division.—Occasionally, the artery is divided for a short distance at its upper part into two trunks, which are united below. Frequently the artery divides at a higher level than usual, and the vessels concerned in this high division are three, viz., radial, ulnar, and interosseous. Most frequently the radial is given off high up, the other limb of the bifurcation consisting of the ulnar and interosseous; in some instances the ulnar arises above the ordinary level, and the radial and interosseous form the other limb of the division; occasionally the interosseous arises high up. Sometimes, long slender vessels, vasa aberrantia, connect the brachial or the axillary artery with one of the arteries of the forearm, or branches from them. These vessels usually join the radial. Varieties in Muscular Relations.—The brachial artery is occasionally concealed, in some part of its course, by muscular or tendinous slips derived from the Coracobrachialis, Biceps brachii, Brachialis, or Pronator teres. Collateral Circulation.—After the application of a ligature to the brachial artery in the upper third of the arm, the circulation is carried on by branches from the humeral circumflex and subscapular arteries anastomosing with ascending branches from the profunda brachii. If the artery be tied below the origin of the profunda brachii and superior ulnar collateral, the circulation is maintained by the branches of these two arteries anastomosing with the inferior ulnar collateral, the radial and ulnar recurrents, and the dorsal interosseous. Branches.—The branches of the brachial artery are: Profunda Brachii. Superior Ulnar Collateral. Nutrient. Inferior Ulnar Collateral. Muscular. 1. The arteria profunda brachii (superior profunda artery) is a large vessel which arises from the medial and back part of the brachial, just below the lower border of the Teres major. It follows closely the radial nerve, running at first backward between the medial and lateral heads of the Triceps brachii, then along the groove for the radial nerve, where it is covered by the lateral head of the Triceps brachii, to the lateral side of the arm; there it pierces the lateral intermuscular septum, and, descending between the Brachioradialis and the Brachialis to the front of the lateral epicondyle of the humerus, ends by anastomosing with the radial recurrent artery. It gives branches to the Deltoideus and to the muscles between which it lies; it supplies an occasional nutrient artery which enters the humerus behind the deltoid tuberosity. A branch ascends between the long and lateral heads of the Triceps brachii to anastomose with the posterior humeral circumflex artery; a middle collateral branch descends in the middle head of the Triceps brachii and assists in forming the anastomosis above the olecranon; and, lastly, a radial collateral branch runs down behind the lateral intermuscular septum to the back of the lateral epicondyle of the humerus, where it anastomoses with the interosseous recurrent and the inferior ulnar collateral arteries. 2. The nutrient artery (a. nutricia humeri) of the body of the humerus arises about the middle of the arm and enters the nutrient canal near the insertion of the Coracobrachialis. 
FIG. 526 - Diagram of the anastomosis around the elbow-joint. 3. The superior ulnar collateral artery (a. collateralis ulnaris superior; inferior profunda artery), of small size, arises from the brachial a little below the middle of the arm; it frequently springs from the upper part of the a. profunda brachii. It pierces the medial intermuscular septum, and descends on the surface of the medial head of the Triceps brachii to the space between the medial epicondyle and olecranon, accompanied by the ulnar nerve, and ends under the Flexor carpi ulnaris by anastomosing with the posterior ulnar recurrent, and inferior ulnar collateral. It sometimes sends a branch in front of the medial epicondyle, to anastomose with the anterior ulnar recurrent. 4. The inferior ulnar collateral artery (a. collateralis ulnaris inferior; anastomotica magna artery) arises about 5 cm. above the elbow. It passes medialward upon the Brachialis, and piercing the medial intermuscular septum, winds around the back of the humerus between the Triceps brachii and the bone, forming, by its junction with the profunda brachii, an arch above the olecranon fossa. As the vessel lies on the Brachialis, it gives off branches which ascend to join the superior ulnar collateral: others descend in front of the medial epicondyle, to anastomose with the anterior ulnar recurrent. Behind the medial epicondyle a branch anastomoses with the superior ulnar collateral and posterior ulnar recurrent arteries. 5. The muscular branches (rami musculares) three or four in number, are distributed to the Coracobrachialis, Biceps brachii, and Brachialis. The Anastomosis Around the Elbow-joint (Fig. 526).—The vessels engaged in this anastomosis may be conveniently divided into those situated in front of and those behind the medial and lateral epicondyles of the humerus. The branches anastomosing in front of the medial epicondyle are: the anterior branch of the inferior ulnar collateral, the anterior ulnar recurrent, and the anterior branch of the superior ulnar collateral. Those behind the medial epicondyle are: the inferior ulnar collateral, the posterior ulnar recurrent, and the posterior branch of the superior ulnar collateral. The branches anastomosing in front of the lateral epicondyle are: the radial recurrent and the terminal part of the profunda brachii. Those behind the lateral epicondyle (perhaps more properly described as being situated between the lateral epicondyle and the olecranon) are: the inferior ulnar collateral, the interosseous recurrent, and the radial collateral branch of the profunda brachii. There is also an arch of anastomosis above the olecranon, formed by the interosseous recurrent joining with the inferior ulnar collateral and posterior ulnar recurrent (Fig. 529).
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