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The ulnar nerve arises from the medial cord of the brachial plexus, from the eighth cervical and first thoracic nerves. It also occasionally has a root from
Branches to deltoid
Nerve to long
the lateral cord of the plexus (seventh cervical nerve). In the axilla it lies between the axillary artery and vein, and behind the medial cutaneous nerve of the forearm (O.T. internal cutaneous); in the proximal half of the arm it lies on the medial side of the brachial artery anterior to the triceps muscle. In the distal half of the arm it is separated from the brachial artery; and passing behind the intermuscular septum, and in front of the medial head of the triceps in company with the superior ulnar collateral (O.T. inferior profunda) artery, it reaches the interval between the medial epicondyle of the humerus and the olecranon. It is there protected by an arch of deep fascia stretching between the epicondyle and the olecranon. It enters the forearm between the humeral and ulnar origins. of the flexor carpi ulnaris, and courses distally between the flexor carpi ulnaris and flexor digitorum profundus. In the distal half of the forearm it becomes comparatively superficial, lying on the medial side of the ulnar artery, overlapped by the tendon of the flexor carpi ulnaris. Just proximal to the transverse carpal ligament, and lateral to the pisiform bone, it pierces the deep fascia, in company with the artery, and passes into the hand over the transverse carpal ligament. Reaching the palm it divides, under cover of the palmaris brevis muscle, into its two terminal branches, superficial and deep. Branches. The ulnar nerve gives off no branches till it reaches the forearm. In the forearm it gives off articular, muscular, and cutaneous branches.
Proximal branch of dorsal
cutaneous nerve of
Distal branch of dorsal
The articular branch is distributed to the elbow-joint and arises as the nerve passes behind the medial epicondyle of the humerus.
The muscular branches arise as soon as the nerve enters the forearm. They are distributed to the muscles between which the ulnar nerve lies-the flexor carpi ulnaris and the medial half of the flexor digitorum profundus.
The cutaneous branches are two in number, palmar and dorsal.
The palmar cutaneous ramus is variable in size and position. It pierces the deep fascia in the distal third of the forearm and passes to the hypothenar eminence and palm of the hand, to the skin over which it is distributed. It gives branches to the ulnar artery, and communicates often with the medial cutaneous nerve of the forearm and the palmar branch of the median nerve.
The dorsal ramus of the hand is much larger (Fig. 618). It arises from the ulnar nerve in the middle third of the forearm; and, directed obliquely distally and backwards, beneath the tendon of the flexor carpi ulnaris, it becomes cutaneous on the medial side of the forearm in its distal fourth. It passes on to the back of the hand, and, after giving off branches to the skin of the wrist and hand which. communicate with the superficial ramus of the radial nerve, it terminates in two dorsal digital nerves, to supply the little finger and half the ring-finger, in the following way-the medial branch courses along the medial side of the dorsum of the hand and little finger: the lateral branch subdivides at the cleft between the ring and little fingers to supply the adjacent sides of these fingers; this branch communicates with the superficial ramus of the radial nerve. The nerve may supply two and a half fingers on the dorsum of the hand.
Ramus Volaris Manus.-In the palm the ulnar nerve supplies a small muscular branch to the palmaris brevis, and then subdivides into its terminal branches, which are named superficial and deep.
Ramus Superficialis.-The superficial branch is purely cutaneous; it passes distally deep to the palmar aponeurosis, and subdivides into a medial and a lateral branch. The medial branch courses along the medial border of the little finger, which it supplies on its palmar aspect. The lateral branch (common volar digital nerve) becomes superficial at the cleft between the fourth and fifth fingers, between the slips of the palmar aponeurosis, and subdivides into two branches (proper volar digital nerves) which supply the adjacent sides of these fingers on their palmar aspect. It communicates with the adjacent digital branch of the median nerve.
Ramus Profundus.-The deep branch is purely muscular. It separates from the superficial branch, and passes deeply between the flexor brevis and abductor digiti quinti muscles; it supplies those muscles and the opponens digiti quinti, and, turning laterally along the line of the deep palmar arch and under cover of the deep flexor tendons, it supplies branches to the following muscles: interossei, thirdand fourth lumbricales (on their deep surfaces), the adductor pollicis (oblique and transverse parts), and the interosseus primus volaris (deep part of the flexor pollicis brevis).
Communications.-The ulnar nerve communicates (1), in some cases, with the median nerve in the forearm; (2) with the medial cutaneous nerve of the forearm, and sometimes with the median nerve, by its palmar branch; (3) with the cutaneous part of the median nerve in the palm, by means of its terminal cutaneous branches; (4) with the superficial ramus of the radial nerve on the dorsum of the hand, by means of its dorsal branch.
NERVUS CUTANEUS ANTIBRACHII MEDIALIS.
The medial cutaneous nerve of the forearm (O.T. internal cutaneous nerve) arises from the medial cord of the brachial plexus, from the eighth cervical and first thoracic nerves (Figs. 614 and 617). In the axilla and proximal half of the arm it lies superficial to the main artery. It becomes cutaneous by piercing the deep fascia about the middle of the arm on its medial side, and accompanying the basilic vein through the distal half of the arm, it divides at the front of the elbow into its two terminal branches.
Branches. In the arm, as soon as it becomes superficial, the nerve gives off a branch which supplies the skin of the distal half of the anterior surface of the
arm on its medial side. At the elbow it divides into two terminal branchesvolar and ulnar, which, crossing superficial or deep to the median basilic vein, are distributed to the medial side of the forearm.
The volar branch can be followed to the wrist and supplies the whole of the volar surface of the forearm in the medial half; the ulnar branch is not so large, and, passing obliquely backwards and distally over the origins of the pronator and flexor muscles, it is distributed to the proximal two-thirds or three-fourths of the dorsal aspect of the forearm on the medial side.
Communication. The medial cutaneous nerve of the forearm communicates with the volar branch of the ulnar nerve in the distal part of the forearm.
NERVUS CUTANEUS BRACHII MEDIALIS.
The medial cutaneous nerve of the arm (O.T. lesser internal cutaneous nerve arises from the medial cord of the brachial plexus, and ultimately from the first thoracic nerve (Fig. 614, p. 701). It lies at first between the axillary artery and vein; and after descending over, under, or even, in some cases, through the axillary vein, it perforates the deep fascia and is distributed to the skin of the arm for the proximal half or more on its medial side.
The nerve varies considerably in size. It may be absent, its place being taken by branches of the intercosto-brachial or by branches from the posterior cutaneous branch of the radial nerve. It generally bears a distinct relation in size to the intercosto-brachial, due to the fact that the size of the latter depends upon the size of the part of the second thoracic nerve connected with the first in the thorax. If an intra-thoracic connexion occurs between the first and second thoracic nerves, the intercosto-brachial may be deprived of a certain number of its fibres, which in that case reach the upper limb through the medial cutaneous nerve of the arm.
When traced up to the plexus the medial cutaneous nerve of the arm is found to have an origin from the posterior part of the cord formed by the eighth cervical and first thoracic nerves, and usually receives fibres from the first thoracic nerve only. In cases where "axillary arches" are present they may be supplied by this nerve.
The axillary nerve (O.T. circumflex) at its origin is just below the suprascapular and comes from the same spinal nerves-the fifth and sixth cervical nerves (Fig. 614, p. 701). Extending distally and laterally behind the axillary artery, it leaves the axilla by passing round the lateral border of the subscapularis muscle, in company with the posterior circumflex artery of the humerus, in a quadrilateral space bounded by the humerus, subscapularis, triceps (long head), and teres major. Winding round the surgical neck of the humerus from medial to lateral side, it terminates by supplying the deltoid muscle (Fig. 619, p. 708).
Branches. Muscular branches are supplied to the teres minor and deltoid muscles. The nerve to the teres minor enters the lateral aspect of the muscle. It possesses a pseudo-ganglion, a thickening of fibrous tissue, on its trunk.
Articular branches enter the posterior part of the capsule of the shoulder-joint. A cutaneous branch of considerable size-the lateral cutaneous nerve of the armpasses obliquely distally and forwards from beneath the deltoid muscle, becoming superficial at its posterior border. Sometimes branches pierce the muscle. It supplies the skin over the insertion of the deltoid and the proximal half of the arm on its lateral aspect (Figs. 617, p. 706, and 618, p. 707).
The radial nerve (O.T. musculo-spiral) appears to be the continuation into the upper limb of the posterior cord of the brachial plexus. It usually takes origin from all the nerves which form the posterior cord-the fifth, sixth, seventh, and eighth cervical and first thoracic nerves (Fig. 614, p. 701). In some cases the first thoracic contributes no fibres, and often the fifth cervical nerve is excluded It extends from the axilla, round the back of the humerus, to the bend of from it. the elbow, where it ends by dividing into its superficial and deep terminal branches.
In the axilla it lies behind the axillary artery, and in front of the subscapularis, teres major, and latissimus dorsi muscles.
In the arm, in the proximal third, it lies to the medial side of the humerus, behind the brachial artery, and upon the long head of the triceps. In the middle third of the arm it courses obliquely laterally and distally .in the radial groove of the humerus, along with the profunda brachii artery, separating the long, lateral, and medial heads of the triceps muscle (Fig. 619, p. 708). In the distal third of the arm, piercing the proximal part of the intermuscular septum at the lateral border of the triceps muscle, it passes to the bend of the elbow in front of the lateral epicondyle of the humerus, in the interval between the brachio-radialis and brachialis muscles. Under cover of the former muscle, in the hollow of the elbow, it divides into its two terminal branches, the superficial and deep rami.
The collateral branches are in three sets, arising (a) on the medial side, (b) on the back, and (c) on the lateral side of the humerus (Fig. 620).
I. Branches arising medial to the Humerus. 1. N. cutaneus brachii posterior (O.T. upper internal cutaneous branch of musculo-spiral).-The posterior cutaneous nerve of the arm, arising in common with one of the following, or independently, pierces the fascia on the medial side of the arm near the axilla. It supplies the skin of the posterior surface of the arm in the proximal third, proximal and posterior to the area supplied by the medial nerve of the arm (O.T. lesser internal cutaneous) (Fig. 618, p. 707). This nerve varies in size, according to the bulk of the lastnamed and the intercosto-brachial nerves.
2. Rami Musculares.-The muscular branches are
in two sets. One series supplies the long head of the triceps muscle near its origin; the other series enters the medial head of the muscle. One of the latter, separating itself from the rest, accompanies the ulnar nerve in the middle third of the arm, and supplies the distal part of the muscle. This is sometimes
called the collateral ulnar nerve.
II. Branches arising on the Posterior Surface of the Humerus.-Muscular branches arise from the nerve in the radial groove for the supply of all three heads of the triceps muscle. The branch which enters the medial head of the muscle, besides supplying it, passes through the muscle and behind the lateral epicondyle of the humerus, to terminate in
POSTERIOR CUTANEOUS BRANCH
TO TRICEPS MEDIAL HEAD
SENTATION OF THE BRANCHES OF
III. Branches arising at the Lateral Side of the FIG. 620.-DIAGRAMMATIC REPREHumerus.-1. The dorsal cutaneous nerve of the forearm consists of two branches, proximal and distal. Arising from the radial nerve before it pierces the lateral intermuscular septum, these branches pierce the deep fascia close together on the lateral side of the arm in its distal half. Passing distally over the back of the lateral epicondyle, the proximal branch supplies the skin of the lateral side and posterior surface of the arm in its distal third, and the dorsal surface of the forearm in its proximal half. The distal branch supplies an area of skin on the dorsal surface of the forearm in the proximal two-thirds, medial to the area innervated by the musculo-cutaneous nerve (Fig. 618, p. 707).
2. Muscular Branches.-The radial nerve, as it lies in the interval between the brachialis and brachio-radialis muscles, supplies a small branch to the brachialis (which in some cases is not present) and nerves to the brachio - radialis and extensor carpi radialis longus. It may also provide the nerve to the extensor carpi radialis brevis.
RAMUS SUPERFICIALIS NERVI RADIALIS.
The superficial ramus (O.T. radial nerve) is entirely cutaneous in its distribution. Arising in the hollow of the elbow beneath the brachio-radialis, it courses
Muscular branches to superficial muscles.
Muscular branch to abductor pollicis longus,
Terminal branch to carpal joints
FIG. 621.-DISTRIBUTION OF THE DEEP BRANCH OF THE
distally under cover of that muscle through the proximal two-thirds of the forearm, and accompanies the radial artery in the middle third of the forearm. It then passes backwards, under cover of the tendon of the brachio-radialis, and pierces the deep fascia on the lateral aspect of the forearm in the distal third. It is distributed to the skin of the dorsum of the wrist, the lateral side and the dorsum of the hand, and the dorsum of the thumb and lateral two and a half fingers (Fig. 618, p. 707). Its branches communicate, on the ball of the thumb, with the musculo-cutaneous nerve, and, on the dorsum of the hand, with the dorsal branch of the ulnar nerve (ramus anastomoticus ulnaris). The digital nerves are small, and Two are five in number. pass to the back of the thumb and reach the level of the inter-phalangeal articulation. One supplies the lateral side of the index finger as far as the second phalanx. The remaining two branches divide at the clefts between the second and third, and third and fourth fingers respectively, and innervate the adjacent sides of those fingers as far as the second phalanx. The rest of the skin of those digits to the tips is supplied by digital branches of the median nerve. The nerve may only supply the thumb and one and a half fingers, being replaced by branches from the ulnar nerve.
The deep ramus (O.T. posterior interosseous nerve) is entirely muscular and articular in its distribution. It arises, like the superficial ramus, under cover of the brachio-radialis muscle. Directed obliquely distally and backwards, it reaches the back of the forearm, after passing round the lateral aspect of the radius, by piercing the fibres of the supinator muscle (Fig. 621). On the dorsal surface of the