The upper extremities include the shoulders, arms, forearms, wrists, and hands and contain each thirty-two bones. The bones of the two shoulders taken together are called the shoulder girdle and consist of the two clavicles or collar bones and the two scapulæ or shoulder blades, which together make an almost complete girdle of the shoulders.

The clavicle is a long slender bone extending almost horizontally from the sternum to the scapula and can be felt for its whole length in the living. For the inner two-thirds it is convex anteriorly, for the outer third concave. In woman it is generally less curved, smoother, and more slender than in man, and as bone is rough when the muscles attached are powerful, the right clavicle, being used more, is generally rougher and thicker than the left. Among the muscles attached are the large neck muscle, the sterno-cleido-mastoid, whose tendons form the presternal notch, the trapezius, the pectoralis major, and the deltoid.

Being slender and superficial the clavicle is most frequently broken of any bone in the body, generally by indirect violence, as by falling with the hand out, though old people in such a case are apt to get Colles’ fracture at the wrist. The bone generally gives way at the juncture of the outer and middle thirds, with displacement of the parts inward, so that the fracture is seldom compound. Since, however, the main vessels of the upper arm, with their nerves, lie beneath the clavicle, there is danger of their being punctured. Such serious injury is guarded against by the presence of the subclavius muscle. The clavicle is occasionally removed for sarcoma.

The scapula or shoulder blade, so called from its shape, is a large, flat, triangular bone with a prominent ridge, the spine, crossing its dorsum or posterior surface near its upper edge. It extends from the second to the seventh rib, with its posterior margin parallel to and about one inch from the dorsal vertebræ. The head, in which is situated the glenoid cavity for articulation with the humerus or upper arm bone, is surrounded by a slight constriction, the neck. Above it projects the coracoid process, so called from its fancied resemblance to a crow’s beak. This can usually be felt about one inch from the juncture of the outer and middle thirds of the clavicle and from it arise the short head of the biceps and the coraco-brachialis muscle. The acromion process at the end of the spine extends out beyond the glenoid cavity posteriorly and affords attachment to the deltoid and trapezius muscles. It forms the summit of the shoulder. Numerous other muscles are attached to the surface of the scapula, the only parts which are truly subcutaneous being the whole length of the spine and the acromion process, though the lower angle and the coracoid process can generally be felt. The muscles bulge so much that the spine in the living appears as a slight depression extending back almost to the vertebræ. The large number of the muscles on the shoulder and arm is due to the great flexibility and strength required for the various uses to which the arms are put.

Shoulder Muscles.—The most important shoulder muscle is the deltoid, a large triangular muscle, which surrounds and protects the shoulder-joint and gives the shoulder its rounded form. It rises from the outer third of the clavicle, from the acromion process, and from the whole length of the spine of the scapula, and is inserted by a tendon into a rough prominence on the middle of the outer side of the humerus. It serves to raise the arm and to draw it somewhat forward or back, according as the anterior or posterior fibers are used. The pectoralis major rises from the inner half of the clavicle, the front of the sternum, and the cartilages of the true ribs and its fibers converge to form a fan-shaped muscle, which is inserted by a flat tendon into the edge of the bicipital groove on the humerus. It draws the arm forward and inward and helps considerably in forced inspiration. The serratus magnus rises from the outer surface and upper border of the eight upper ribs and from an aponeurosis covering the upper intercostal spaces, and is inserted along the whole length of the posterior border of the scapula. It carries the scapula forward and is used in pushing.

The scapula is seldom broken because it is quite movable and is covered with large muscles and because it lies on the chest, which serves as an elastic cushion. The acromion process is the part most frequently broken and occasionally the neck is fractured. Tumors occur and may necessitate the amputation of the whole upper extremity.

The Humerus.—The bone of the upper arm, the humerus, is the largest bone in the upper extremity and articulates with the scapula above and with the ulna and radius below. At its upper end are the head and the anatomical neck, with the greater tuberosity external to and the lesser tuberosity in front of them. The constriction of the surgical neck is below the tuberosities, and extending from between them downward and inward along the upper third of the bone is the bicipital groove for the long head of the biceps. Though round above, below the shaft becomes flattened from before backward and curves slightly forward, terminating in the internal and external condyles, from the former of which the flexors and the round pronator arise and from the latter the extensors and supinators. From the external condyle also there projects in front the radial head or capitellum for articulation with the radius. Internally to the capitellum in front and in a corresponding position on the back of the bone are the trochlear surfaces for articulation with the ulna, there being a depression in front called the coronoid fossa for the reception of the coronoid process of the ulna in flexion of the forearm, and another depression behind, the olecranon fossa, to receive the tip of the olecranon process during extension. On the lower half of the humerus at the back is the spiral groove for the musculo-spiral nerve and the superior profunda artery, while the ulnar nerve runs in a groove back of the internal condyle.

The humerus is almost completely covered with muscles, the only part that is subcutaneous being a small portion of the external and internal condyles. The head can be felt under the muscles and the greater tuberosity forms the point of the shoulder. When the arm is at the side, the biceps appears at the front and inner side and the brachialis anticus on either side below, while on the back of the arm, with its largest swelling above, is the triceps.

Upper Arm Muscles.—The biceps is the most important arm muscle. It rises by a short head from the coracoid process of the scapula and by a long head from a tubercle on the upper margin of the glenoid cavity, the tendon arching over the head of the humerus and descending in the bicipital groove. It is inserted into the back of the tuberosity of the radius and by a broad aponeurosis into the fascia of the forearm. It flexes and supinates the forearm and renders the fascia tense. Its inner border forms a guide in tying the brachial artery, as this artery runs along its inner side.

The brachialis anticus rises from the lower half of the outer and inner surfaces of the humerus and is inserted into the coronoid process of the ulna, thus covering and projecting the elbow-joint anteriorly. It is a flexor of the forearm.

Another smaller muscle on the anterior arm, which also aids in flexion, is the coraco-brachialis, which extends from the coracoid process of the scapula to the middle of the inner surface of the humerus.

Extending the entire length of the posterior surface of the humerus is the triceps, similar to the quadriceps extensor in the thigh and direct antagonist to the biceps and brachialis anticus muscles. It rises by a long head from below the glenoid fossa, by the external head from the upper third of the posterior surface of the humerus, and by the internal head from the middle and lower thirds of the posterior surface. It is inserted in the olecranon process of the ulna and serves to extend the forearm and arm.

The humerus is more often fractured by muscular action than any other bone. Usually the fracture occurs in the lower half of the bone and sometimes the musculo-spiral nerve is involved. There is a great tendency to non-union, probably due to interposition of soft parts. Sometimes the break is across and down between the condyles, T-fracture. Involvement of the elbow-joint is more serious than fracture of the humerus alone. Sarcoma of the humerus does occur and may require the removal of the clavicle and scapula as well as of the arm bone itself. In amputation of the humerus in children a long skin flap is left to allow for growth of the bone, as it is liable to grow again.

The Ulna.—In the forearm there are two bones, the ulna and the radius, of which the former is the longer. The ulna is on the inner side of the forearm and its upper end forms the greater part of the articulation with the humerus, as most of the articulation at the wrist is formed by the radius and the inter-articular fibro-cartilage. The head of the ulna is at the lower extremity of the bone and articulates on the outer side with the radius and below with the triangular fibro-cartilage. From its inner side projects the styloid process. The olecranon process forms the upper extremity and presents anteriorly an articular surface, the greater sigmoid cavity, for articulation with the trochlea of the humerus, where it fits into the olecranon fossa during extension. The same articulating surface also covers the coronoid process, a smaller projection below and in front of the olecranon, which fits into the coronoid fossa during flexion. Continuous with the greater sigmoid cavity on the outer side is the lesser sigmoid cavity for articulation with the head of the radius. Under the triceps tendon, which is inserted into the olecranon, is a bursa or sac of synovial membrane, such as occurs in parts where much force is brought to bear.

The Radius.—The radius, or spoke of the wheel, is on the outer side of the forearm and gets its name from the way it turns upon the ulna in pronation. The shaft is larger below than above and is slightly curved longitudinally for greater strength. The upper extremity or head is small and has a slightly concave upper surface for articulation with the radial head of the humerus. It articulates by its sides with the lesser sigmoid cavity and is bound to the ulna by the orbicular ligament, which runs over a smooth articular surface. Below the head is the constriction of the neck with the tuberosity for the biceps tendon to the inner side below. The lower extremity is large and forms the chief part of the wrist-joint, articulating with the semilunar and scaphoid bones of the wrist. From the lower extremity the strong conical styloid process projects externally.

In the living the olecranon process of the ulna is always felt at the elbow and the posterior border of the ulna forms the prominent ridge down the forearm, leading to the styloid process. The head of the radius is felt just below the external condyle and often makes a dimple in the muscles of the forearm. The rest of its upper half is concealed with muscles, but the lower half is easily felt as there are only tendons over it. The styloid process is felt externally. Normally that of the radius is a little lower than that of the ulna, so that in cases of fracture their relative position is of considerable importance as showing the amount of deformity.

The two forearm bones are more frequently broken together than separately and generally by direct violence, the lower fragment being usually drawn up by the action of the flexor and extensor muscles and producing a swelling on the palmar surface of the forearm. Indirect violence usually causes fracture of the radius only. In both cases, but especially in fracture of both bones, there is a tendency for membrane to get between the fragments, so the arm is put up in splints with the hand midway between pronation and supination in order to separate the bones as far as possible. Care must be taken not to have the bandage too tight or gangrene of the fingers may result. In most fractures of the arm it is put up bent, but in fracture of the olecranon it is put up fully extended, as the fragment is sure otherwise to be displaced by the pull of the triceps. In fact, the olecranon is sometimes fractured by the muscular force of the triceps, though usually its fracture, which is frequent, is due to direct violence. The ulna is also often fractured in the middle by direct violence or the styloid process may be broken. Fracture of the neck or shaft of the radius is very common, the most important arm fracture being that of the lower end of the radius or Colles’ fracture. This and the corresponding fracture in the leg, Pott’s fracture, are two of the commonest fractures. In dislocation of the wrist the normal relation of the two styloid processes remains unchanged, but in Colles’ fracture the lower fragment often projects on the back of the hand, making a typical deformity called the silver fork deformity.

The bones of the wrist and hand had best be described before the forearm muscles are taken up, as the muscles of the forearm are distributed largely to the fingers.

The Wrist.—The wrist or carpus is made up of eight bones arranged in two rows of four each. In the first row are the scaphoid and semilunar bones, on the outer side, articulating with the radius, the cuneiform articulating with the fibro-cartilage of the wrist-joint, and the pisiform. In the second row, in corresponding positions, are the trapezium, trapezoid, os magnum, and unciform. The eminence felt on the radial side of the wrist is the protuberance of the scaphoid, while the pisiform is generally felt on the ulnar side.

The Hand.—The hand contains nineteen bones, five metacarpal bones, one for each finger and the thumb, whose bases articulate with the lower row of wrist bones, and fourteen phalanges, three for each finger and two for the thumb, of which the first row articulate with the metacarpal bones. They are all long bones and are slightly concave anteriorly. When the hand is flexed it is the heads of the metacarpal bones, not the bases of the phalanges, that are so prominent, the head of the third metacarpal being most prominent.

The metacarpals are seldom fractured, though bad fractures occasionally occur. In comminuted fracture nothing can be done but remove the bone. If the periosteum is left the bone will grow again. Two diseases sometimes affect the metacarpals and the phalanges, tuberculosis and syphilis. Both cause swelling of the bones.

Muscles of the Forearm.—The chief groups of muscles on the forearm are the flexors and pronators on the anterior surface and the extensors and supinators on the posterior surface. In general the flexors and pronators take their origin from on or around the internal condyle, while the extensors and supinators arise on or around the external condyle. Where not otherwise stated it will be understood that such is their origin. In a general way they may by grouped as follows:

Of the flexors of the wrist the flexor carpi radialis is inserted into the base of the index and usually of the third metacarpal bone, the flexor carpi ulnaris into the fifth metacarpal, the pisiform and the unciform bones, while the palmaris longus goes to the anterior annular ligament of the wrist and the palmar fascia of the hand. The flexor sublimis digitorum is inserted by four tendons into the second phalanges of the fingers, while the flexor profundus digitorum arises from the upper part of the ulna and is inserted into the last phalanges of the fingers. The flexor of the thumb arises from the middle of the radius and is inserted into the last phalanx of the thumb. Which joint is flexed by a muscle depends upon the origin and insertion of the muscle, all those included between being affected. Thus, the flexor sublimis digitorum, which has its origin in part at least from the condyle and is inserted in the second phalanges of the fingers, flexes the forearm, wrist, and all the finger-joints but the last, while the flexor profundus digitorum, arising from the ulna, though it flexes the wrist and fingers, has no power of flexing the forearm.

The pronator radii teres, besides arising from the supra-condylar ridge, rises from the coronoid process of the ulna. It is inserted into the middle of the outer surface of the radius and serves to pronate the forearm. The other pronator, the pronator quadratus, is a small quadrilateral muscle extending transversely across the radius and ulna just above their carpal extremities. It rises from the anterior surface of the ulna and is inserted into the anterior external border of the radius.

On the back of the forearm the anconeus serves to extend the forearm only, being inserted into the upper part of the posterior surface of the ulna. The extensors of the wrist are inserted into the bases of the various metacarpal bones and have some power to extend the forearm as well as the wrist. The extensors of the thumb, as their names imply, go one to the metacarpal bone and one to each of the phalanges, the longest one extending the whole thumb, the others only a part. They rise from the ulna and radius, not the condyle. The extensor communis digitorum goes to all the phalanges of all the fingers, the extensor minimi digiti to those of the little finger only, and the extensor indicis to those of the index finger, the last two arising short of the condyle.

Of the supinators the longer one is inserted into the styloid process of the radius, while the shorter one, the supinator brevis, is inserted into the upper part of the same bone, both thus serving to turn the radius on the ulna.

Where the tendons of the various muscles pass over the wrist, both front and back, they are covered with a synovial sheath and are held down by a broad ligament, which some of them perforate, the annular ligament. The strong fibrous band of the anterior annular ligament arches over the carpal bones in front. Beneath it pass the median nerve and the tendons of the flexors of the fingers and thumb. The posterior annular ligament is of less importance.

The deep palmar fascia forms a sheath for the muscles of the hand. In carpenters there sometimes occurs Dupuytren’s contraction of the palmar fascia, which draws the fingers up. As operation is not always successful, it is quite a serious matter.

The muscles of the hand itself include various abductor, adductor, and short flexor muscles of the thumb and little finger. There also extend between the metacarpal bones the lumbricales, four small muscles that aid the deep flexor muscles; likewise seven interossei, of which four are dorsal and three palmar. The dorsal interossei arise by two heads from the adjacent sides of the metacarpal bones and are inserted into the bases of the first phalanges, thus abducting the fingers; while the palmar interossei, arising from the palmar surface of the second, fourth, and fifth metacarpals, are inserted into the three corresponding first phalanges and adduct the fingers toward an imaginary line drawn through the middle finger.

Joints of the Upper Extremity.—The joints of the upper extremity, with the exception of the wrist-joint, are the most freely movable of any in the body, probably because the hand has the finest work to do and a greater number of motions are required. Even the wrist has much greater freedom of motion than the corresponding joint in the lower extremity.

The shoulder-joint is rather a deep joint, to allow of the varied motion required, and has a capsular ligament from the margin of the glenoid fossa above to the neck of the humerus below. The elbow, which is a hinge joint, has an anterior and a posterior ligament and two lateral ligaments, as is practically the case in all such joints. The wrist has several ligaments which, taken together, are capsular in nature.

Blood Supply of the Upper Extremity.—The blood supply of the upper extremity comes through the subclavian artery, which, on the right, springs from the innominate artery and on the left from the aortic arch. It remains one trunk as far as the elbow, though different names have been given to different parts. Thus, as it passes over the lower border of the first rib, it becomes the axillary, and at the lower border of the axilla, where it starts down the arm, the brachial. At the elbow it divides into the ulnar and radial arteries.

In its upper part the brachial artery lies internal to the humerus but below it is in front of the bone. The radial runs in a line from the middle of the elbow anteriorly to the inner side of the styloid process of the radius and is much exposed to injury in the lower third of its course, as when the hand is thrust through glass. On it at the wrist the pulse is counted. It is much smaller than the ulnar and winds around the outer side of the thumb to the palm, where, with the deep branch from the ulnar, it forms the deep palmar arch. The ulnar artery passes obliquely inward to the middle of the forearm and thence along its ulnar border to the palm of the hand, where it divides into the deep branch and the superficial palmar arch which supplies the four digital arteries.

From the axillary artery branches go to the chest wall and shoulder, the most important being the two circumflex arteries to the deltoid. The brachial has only two branches of any importance, the superior and inferior profunda, both on the upper arm, of course.

In case of hemorrhage compression can frequently be applied with the fingers where the subclavian crosses the rib or in the axilla, where the artery can be pressed up against the humerus.

Nerves.—The nerve supply of the shoulder comes chiefly from the anterior and posterior thoracic, the suprascapular, and the circumflex, these last going to the deltoid. The biceps is supplied by the musculo-cutaneous, the triceps by the musculo-spiral, and the brachialis anticus by both. Most of the flexor and pronator muscles are supplied by the median, while the posterior interosseous and the musculo-spiral nerves go to the extensors and supinators. The ulnar nerve supplies the hand largely.