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the lateral and posterior cords of the brachial plexus and the lateral anterior thoracic nerve. Below and to the medial side is the axillary vein, the medial anterior thoracic nerve intervening.
Relations of the Second Part-Posterior.-Behind the second part of the artery are the posterior cord of the brachial plexus and a layer of fascia which separates it from the subscapularis muscle. Anterior. In front is the pectoralis minor, and, more superficially, the pectoralis major, the fascia and skin. Lateral. To the lateral side lies the lateral cord of the brachial plexus. Medial.—On the medial side the medial cord of the plexus lies in close relation to the artery, and intervenes between it and the axillary vein.
Relations of the Third Part-Posterior.-The third part of the artery rests posteriorly upon the lower border of the subscapularis, the latissimus dorsi, and the teres major. It is separated from the fibres of the subscapularis by the axillary (O.T. circumflex) and radial (O.T. musculo-spiral) nerves, and from the latissimus dorsi and teres major by the radial nerve alone. Anterior.-It is crossed in front by the medial head of the median nerve. In its upper half it lies under cover of the lower part of the pectoralis major, the fascia and skin, whilst its lower part, which is superficial, is covered by skin and fascia only. Lateral.-To the lateral side lie the median and musculo-cutaneous nerves and the coraco-brachialis muscle. Medial.-To the medial side is the axillary vein. The two vessels are, however, separated by two of the chief branches of the medial cord of the brachial plexus, for in the angle between the vein and the artery, and somewhat in front of the latter, lies the medial cutaneous nerve of the forearm (O.T. internal cutaneous nerve); and, in the angle behind is the ulnar nerve. The medial cutaneous nerve of the arm (O.T. lesser internal cutaneous) lies medial to the vein, and the venæ comites of the brachial artery ascend along the medial side, to terminate in the axillary vein at the lower border of the subscapularis muscle.
BRANCHES OF THE AXILLARY ARTERY.
(1) Arteria Thoracalis Suprema. The highest thoracic artery is a small branch which arises from the first part of the axillary at the lower border of the subclavius. It runs downwards and medially, across the first intercostal space, pierces the medial part of the costo-coracoid membrane, and supplies branches to the subclavius, the pectoralis major and minor, and to the serratus anterior (O.T. magnus) and the intercostal muscles; it anastomoses with branches of the transverse scapular, the internal mammary, and the thoraco-acromial arteries.
(2) Arteria Thoracoacromialis.-The thoraco-acromial artery (Fig. 766) arises near the upper border of the pectoralis minor, from the second part of the axillary artery. It is a very short trunk, of considerable size, which passes forwards. pierces the costo-coracoid membrane, and terminates, deep to the clavicular portion of the pectoralis major, by dividing into four terminal branches-clavicular, pectoral, deltoid, and acromial.
(a) The clavicular branch is a long slender artery which runs upwards and medially, to the sterno-clavicular joint, anastomosing with the supreme thoracic, with branches of the transverse scapular, and with the first perforating branch of the internal mammary artery. It supplies the adjacent muscles and the sterno-clavicular articulation.
(b) The pectoral is a large branch which descends between the two pectoral muscles, to both of which it gives branches, and it anastomoses with the intercostal and lateral thoracic arteries.
(c) The deltoid branch runs distally, in the groove between the pectoralis major and the deltoid, where it lies by the side of the cephalic vein, as far as the insertion of the deltoid. It anastomoses with the acromial branch and with the anterior circumflex artery, and it gives branches to the pectoralis major and deltoid muscles and to the skin.
(d) The acromial branch runs upwards and laterally, across the tip of the coracoid process, to the acromion; it anastomoses with the deltoid branch, with the acromial branches of the transverse scapular, and with the posterior circumflex arteries. It gives
branches to the deltoid.
(3) Arteria Thoracalis Lateralis.-The lateral thoracic artery arises from the second part of the axillary, and descends, along the lower border of the pectoralis minor, to anastomose with the intercostal and subscapular arteries and with the pectoral branch of the thoraco-acromial. It supplies the adjacent muscles, and sends mammary branches to the lateral part of the corresponding mammary gland.
(4) Arteria Subscapularis.-The subscapular artery is the largest branch of the axillary artery. It arises from the third part of the artery, opposite the lower border of the subscapularis, along which it descends, giving branches to the muscle and to the medial wall of the axillary space. After a short course it divides into two terminal branches, the circumflexa scapula and the thoraco- dorsalis.
(1) The circumflex scapulæ is frequently the larger branch. It arises about 37 mm. (one and a half inches) from the commencement of the subscapular trunk, and passes backwards into the triangular space which lies between the subscapularis above, the teres major below, and the long head of the triceps laterally. Turning round, and usually grooving the axillary border of the scapula, under cover of the teres minor, it enters the infraspinous fossa, where it breaks up into branches which anastomose with branches of the descending branch of the transverse cervical artery and the transverse scapular arteries. Whilst it is in the triangular space the artery gives off an infrascapular branch which passes into the subscapular fossa and terminates by anastomosing with the branches of the descending branch of the transverse cervical and the transverse scapular arteries. It gives off, in the same situation, a descending branch also, which runs downwards, to the lower angle of the scapula, between the teres major and minor muscles, and small branches are given to the deltoid and long head of triceps.
(2) The thoraco-dorsal continuation of the subscapular trunk accompanies the thoracodorsal nerve (O.T. long subscapular) along the axillary border of the scapula to the wall of the thorax, where it anastomoses with the lateral thoracic artery and with branches of the intercostal arteries.
(5) Arteria Circumflexa Humeri Posterior. The posterior circumflex artery arises from the third part of the axillary artery and passes backwards, accompanied by the axillary nerve, through an intermuscular cleft, the so-called quadrilateral space, which is bounded by the teres minor and subscapularis above, the teres major below, the long head of the triceps medially, and the humerus laterally. It turns round the surgical neck of the humerus, under cover of the deltoid muscle, and terminates in numerous branches which supply the deltoid. As a rule it is an artery of large size, only slightly smaller than the subscapular.
Branches. (a) Muscular to the teres major and minor, the long and lateral heads of the triceps, and the deltoid; (b). An acromial branch, which ascends to the acromion, where it anastomoses with the acromial branches of the transverse scapular and the thoraco-acromial arteries; (c) A descending branch, which runs distally, along the lateral head of the triceps, to anastomose with the profunda artery; (d) Articular to the shoulder-joint; (e) Nutrient to the head of the humerus; (f) Terminal, which supply a large portion of the deltoid, and anastomose with the anterior circumflex and thoraco-acromial arteries.
(6) Arteria Circumflexa Humeri Anterior.-The anterior circumflex artery is a small branch; it is given off from the third part of the axillary close to, or in common with, the posterior circumflex. It passes laterally, posterior to the coraco-brachialis and the two heads of the biceps, round the front of the surgical neck of the humerus, and it terminates by anastomosing with the posterior circumflex. At the intertubercular groove it gives a well-marked branch which accompanies the tendon of the long head of the biceps, supplying the sheath of the tendon, and giving branches to the shoulder-joint. It also gives muscular branches to the adjacent muscles, one of which runs distally along the tendon of insertion of the pectoralis major.
The brachial artery is the direct continuation of the axillary. It commences at the lower border of the teres major, and ends, in the cubital fossa, at the level of the neck of the radius, by dividing into the radial and ulnar arteries. The general course of the brachial artery is distally and laterally, along the medial side of the arm, at first on the medial side and then in front of the humerus. Its position and that of the axillary artery may be indicated on the
surface, when the arm is abducted, by a line drawn from the middle of the clavicle to the centre of the bend of the elbow.
Relations-Posterior.-It lies, successively, anterior to the long head of the triceps, the radial (O.T. musculo-spiral) nerve and the profunda vessels intervening; the medial
head of the triceps; the insertion of the coracobrachialis; and the brachialis. Anterior.-It is overlapped anteriorly by the medial border of the biceps; it is crossed, at the middle of the arm, by the median nerve, and, in addition, it is covered by deep and superficial fascia and skin. In the cubital fossa a thickened portion of the deep fascia, the lacertus fibrosus (0.T. semilunar or bicipital fascia), separates it from the median basilic vein and the volar branch of the medial cutaneous nerve of the forearm, both of which lie in the superficial fascia. Lateral.To the lateral side it is in relation, proximally, with the median nerve, and, distally, with the biceps. Medial. To the medial side it is in relation, in the proximal part of its extent, with the basilic vein, the medial cutaneous nerve of the forearm, the medial cutaneous nerve of the arm, and the ulnar nerve, and in the distal part with the median nerve. Two venæ comites, a media! and a lateral, accompany the artery, and communications between these pass across the vessel.
BRANCHES OF THE BRACHIAL ARTERY.
(1) Arteria Profunda Brachii. - The profunda artery of the arm (O.T. superior profunda) is a large branch which arises from the postero-medial aspect of the brachial, soon after its commencement. It runs distally and laterally, with the radial (O.T. musculo-spiral) nerve, in the radial sulcus (O.T. musculo- spiral groove), and divides, at the back of the humerus, into two terminal branches, anterior and posterior. Not infrequently the division takes place at a higher level, and the artery appears double. The anterior terminal branch accompanies the radial nerve through the lateral intermuscular septum, and passes distally, between the brachio-radialis and the brachialis, to the front of the lateral epicondyle, where it anastomoses with the radial recurrent artery. The posterior terminal branch continues distally, behind the lateral intermuscular septum, and anastomoses, posterior to the lateral epicondyle, with the interosseous recurrent artery and with the inferior ulnar collateral artery. Whilst they are posterior to the humerus one of the terminal branches gives off (a) a slender medial collateral twig, which descends in the substance of the medial head of the triceps to the back of the elbow, where it anastomoses with the inferior ulnar collateral artery; (b) a nutrient branch, which enters a foramen on the posterior surface of the humerus; and (c) an ascending branch, which anastomoses with the descending branch of the posterior circumflex artery.
FIG. 767.-THE BRACHIAL ARTERY AND ITS
(2) Muscular branches are given to the biceps, coraco-brachialis, brachialis, triceps, and pronator teres.
(3) Nutrient.-A small artery which arises from the middle of the brachial and enters the nutrient foramen on the antero-medial surface of the body of the humerus.
(4) Arteria Collateralis Ulnaris Superior.-The superior ulnar collateral artery (O.T. inferior profunda) is smaller than the profunda, with which it sometimes arises by a common trunk; usually, however, it springs from the postero-medial aspect of the middle of the brachial artery. It runs distally and posteriorly, with the ulnar nerve, through the medial intermuscular septum, and then, passing more vertically, reaches the back of the medial epicondyle of the humerus, where it terminates by anastomosing with the dorsal and volar ulnar recurrent and inferior ulnar collateral arteries.
(5) Arteria Collateralis Ulnaris Inferior.-The inferior ulnar collateral artery (O.T. anastomotic) arises from the medial side of the brachial artery about 50 mm. (2 inches) above its termination. It runs medially, posterior to the median nerve and anterior to the brachialis. Then it pierces the medial intermuscular septum, and turns laterally, between the medial head of the triceps and the posterior surface of the bone, to the lateral epicondyle. It supplies the adjacent muscles and anastomoses, anterior to the medial epicondyle, with the volar ulnar recurrent, behind the medial epicondyle with the dorsal ulnar recurrent and the superior ulnar collateral, at the middle of the back of the humerus with the medial collateral branch of the profunda, and posterior to the lateral epicondyle with the posterior terminal branch of the profunda and with the interosseous recurrent artery.
The radial artery (Figs. 768, 769, and 770) is the smaller of the two terminal branches of the brachial artery, but it is the more direct continuation of the parent trunk. It commences, in the cubital fossa, opposite the neck of the radius, and terminates in the palm of the hand, by anastomosing with the deep branch of the ulnar artery, and thus completing the deep volar arch (O.T. palmar).
The trunk is divisible into three parts.
The first part lies in the volar part of the forearm. It runs distally and somewhat laterally to the apex of the styloid process of the radius. The second part curves round the lateral side of the wrist, and across the back of the os multangulum majus, to reach the proximal end of the first interosseous space. The third part passes volarwards, through the first interosseous space, to the palm of the hand, where it joins the deep branch of the ulnar artery.
Relations of the First Part-Dorsal.-It passes successively across the volar aspects of the following structures: the tendon of insertion of the biceps, the supinator, the pronator teres, the radial portion of the flexor digitorum sublimis, the flexor pollicis longus, the pronator quadratus, and the volar ligament of the wrist-joint.
Volar. The artery is covered superficially, in the proximal half, by the volar border of the brachio-radialis; in the remainder of its extent it is covered only by skin and fasciæ. To the radial side are the brachio-radialis, and the superficial branch of the radial nerve (O.T. radial nerve). The nerve lies quite near to the middle third of the artery. To the ulnar side are the pronator teres, proximally, and the flexor carpi radialis, distally. Two venæ comites, one on each side, accompany the artery.
Branches of the First Part.-(1) The radial recurrent arises in the cubital fossa where it springs from the lateral side of the radial, on the volar surface of the supinator. It runs towards the radial border of the forearm, passes between the superficial and deep divisions of the radial (musculo-spiral) nerve, and then runs proximally to the lateral epicondyle of the humerus, where it anastomoses with the anterior terminal branch of the profunda. The radial recurrent supplies numerous muscular branches to the brachio-radialis, the supinator, the extensor carpi radialis longus, and the extensor carpi radialis brevis.
(2) Muscular branches to the muscles on the radial side of the volar aspect of the forearm.
(3) The superficial volar branch (Fig. 768) is a slender vessel which arises a short distance proximal to the wrist and runs distally, across the ball of the thumb. It usually pierces the superficial muscles of the thenar eminence, and terminates either in their substance or by uniting with the ulnar artery and completing the superficial arch of the palm of the hand.
(4) A volar carpal branch passes ulnarwards, between the flexor tendons and their synovial sheaths, and the radial attachments of the volar carpal ligaments. It anastomoses with the volar carpal branch of the ulnar artery to form the volar carpal arch,
and it receives communications from the volar interosseous artery and from the deep volar arch.
Relations of the Second Part. As it curves round the radial side and the dorsum of the wrist, the radial artery lies upon the radial collateral ligament of the intercarpal joint and upon the back of the os multangulum majus. It is crossed by the abductor pollicis longus, the extensor pollicis brevis, and the extensor pollicis longus; more superficially it is covered by skin, and by fascia, which contains the cephalic vein and some filaments of the superficial branch of the radial nerve.
Branches of the Second Part-(1) Dorsales Pollicis. -Two small arteries which run along the borders of the dorsal aspect of the thumb; they supply the skin, tendons, and joints, and anastomose with the volar digital arteries.
(2) Dorsalis Indicis Radialis.A slender artery which runs distally, on the ulnar head of the first dorsal interosseous muscle and along the dorsal aspect of the radial border of the index-finger.
(3) and (4) The first dorsal metacarpal and the dorsal radial carpal arise by a common trunk which crosses deep to the extensor pollicis longus.
(a) The metacarpal branch passes distally, on the dorsal aspect of the second dorsal interosseous muscle, and divides, opposite the heads of the metacarpal bones, into two dorsal digital branches which supply the adjacent sides of the index and middle fingers (b) The dorsal carpal branch runs ulnarwards, on the dorsal carpal ligaments, deep to the extensor tendons, to anastomose with the dorsal carpal branch of the ulnar artery, and to complete the dorsal carpal arch which receives the terminations of the volar and dorsal interosseous arteries. The dorsal carpal arch gives off the second and third dorsal metacarpal arteries, which run distally, on the dorsal aspects of the third and fourth dorsal interosseous muscles, as far as the heads of the metacarpal bones, where each divides into two dorsal digital branches for the adjacent sides of the third and fourth and the fourth and fifth digits, respectively, Each dorsal metacarpal artery is connected with the deep volar (palmar) arch by a proximal perforating branch which passes through the proximal part of the corresponding interosseous space, and with a digital branch from the superficial volar (palmar) arch by a distal perforating branch which passes through the distal part of the space.
FIG. 768.-SUPERFICIAL DISSECTION OF THE VOLAR ASPECT OF THE FOREARM AND HAND, showing the radial and ulnar arteries and the superficial volar arch with its branches.