Position

The hand lying upon its dorsal aspect with the thumb strongly abducted, and the fingers extended.

I. Skin Incisions

1. Along the median line of the palm from the line marking the junction of the wrist with the forearm, to the centre of the root of the middle finger.

2. Transverse incisions from the upper end of No. 1, to the inner and outer borders of the forearm respectively.

3. Transverse incisions from the lower end of No. 1, along the roots of the fingers to the inner and outer borders of the hand. Reflect the flaps inwards and outwards, and expose the superficial fascia, containing granular fat, and—

1. The Superficial Transverse ligament across the roots of the fingers.

2. The Palmaris brevis muscle, along the inner border of the hand.

3. The filaments of the Musculo-cutaneous nerve over the ball of the thumb.

4. The Cutaneous Palmar branch of the Median nerve passing down over the centre of the Annular ligament and along the centre of the palm, and communicating with:

5. The Cutaneous Palmar branch of the Ulnar nerve, which lies over the Ulnar artery and supplies the skin of the inner border of the hand.

6. Unnamed twigs of the Median and Ulnar nerves to the skin of the palm, and small branches of artery from the Superficial Palmar arch.

II

Remove the superficial fascia, the cutaneous nerves, and the Palmaris brevis muscle. The branch of nerve to the muscle from the Ulnar will be divided. There will now be exposed—

1. The Anterior Annular ligament across the wrist.

2. The Palmar fascia. This will be seen to be made up of three divisions, a central thick triangular portion, and two lateral parts covering the Thenar and Hypothenar eminences. The central portion has its apex at the Annular ligament, and its base is cut into four processes, one for each of the fingers. These are connected together by the Superficial Transverse ligament which crosses them at the roots of the fingers.

3. The commencements of the sheaths of the Flexor tendons are seen, and these are found to be joined by the Digital processes of the Palmar fascia.

4. The tendon of the Palmaris longus muscle is seen passing over the Annular ligament to join the apex of the central triangular division of the Palmar fascia.

5. In the intervals of the four Digital processes of the Palmar fascia, the following structures are seen:— a. Small portions of the Lumbricales muscles in each space.

b. The Digital vessels, and nerves. Those supplying the outer side of the index and the inner side of the little fingers emerge from the Palmar fascia further back than the others. The nerves are superficial to the arteries at the clefts of the fingers. The origins of the vessels and nerves are not traceable at this stage.

6. The Ulnar artery and nerve are found beneath the Palmaris brevis muscle, lying at first upon the Annular ligament, and then passing beneath the Palmar fascia. The nerve is on the Ulnar side of the artery.

III

Remove now the three portions of the Palmar fascia and the Superficial Transverse ligament. This must be done carefully, so as to avoid cutting the various vessels and nerves, which are now to be traced to their several origins. There will now be exposed—

1. The small muscles of the thumb. The Abductor most superficial. The outer head of the Flexor brevis along its inner border. A small piece of the Opponens along its outer border, close to the Annular ligament. A small portion of the Adductor running transversely in the cleft between the thumb and index finger, internal to the Flexor brevis pollicis.

2. The small muscles of the little finger. The Abductor most internal. The Flexor brevis along the outer side of the preceding.

3. A small piece of the Abductor indicis muscle along the Radial side of the index finger, emerging from beneath the Adductor pollicis muscle.

4. The tendons of the Flexor sublimis digitorum muscle, entering their sheaths on the four fingers.

5. The four Lumbricales muscles, the first on the Radial side of the index tendon of the Flexor sublimis digitorum muscle, and the others in the intervals between the tendons.

6. The Superficial Palmar arch and its venæ comites crossing transversely the Flexor tendons on a level with the upper border of the abducted thumb. It is formed for the most part by the Ulnar artery, and is completed internally by the Superficialis Volæ branch of the Radial artery, and by a communication with the Radialis Indicis artery. The first of these two last vessels is usually very small and even inconstant, when present it passes over or through the short muscles of the thumb. From the convexity of the arch, which is directed towards the fingers, the Digital branches arise. These are four in number, a single one to the inner side of the little finger, and three others which bifurcate for the contiguous sides of the ring and little, and two next digits. From the concavity of the arch arise small branches to the palm, which have been divided. Close to the lower border of the Annular ligament the Profunda branch of the Ulnar artery arises, and is seen passing between the Flexor brevis and Abductor minimi digiti muscles.

7. Issuing from beneath the Flexor brevis and Adductor pollicis muscles, and lying upon the Abductor indicis muscle is seen the Radialis Indicis branch of the Radial artery, along the outer side of the first finger. The commencement of the Princeps Pollicis branch of the same artery may be seen just at the cleft of the thumb and index finger.

8. The Ulnar nerve is seen to divide close to the lower border of the Annular ligament into a Superficial and Deep branch. The Deep branch passes, with the corresponding branch of the Ulnar artery, between the Flexor brevis and Abductor minimi digiti muscles. The Superficial branch supplies an undivided offset to the inner side of the little finger, and a bifurcated branch to the contiguous sides of this digit, and the next. This last branch also sends an offset of communication beneath the Ulnar artery to the Median nerve. The branches from the Superficial division of the Ulnar nerve to the Palmaris brevis, and integument of the inner border of the palm are, of course, divided.

9. The Median nerve is seen passing from beneath the lower border of the Annular ligament lying upon the Flexor tendons. Just at this point it is found to be flattened out, and divided into two parts of nearly equal size. From the outer part filaments are traceable to the Abductor, Opponens, and outer head of the Flexor brevis pollicis muscles, and the following Digital branches,—viz., two undivided, one for each border of the thumb, and a third also single, for the Radial border of the index finger. This last also supplies the outermost Lumbrical muscle. The inner division supplies two branches which bifurcate for the contiguous sides of the index and middle, and middle and ring fingers; the outermost of these two supplies the next Lumbrical muscle, the innermost communicates with the Ulnar nerve, as mentioned above.

The branches of the Median nerve lie beneath the Superficial Palmar arch.

IV

a. Divide now the Superficial Palmar arch, both internally and externally, raise the included piece, draw it with the Digital branches toward the fingers, and fix it there.

b. Cut through the Superficial branch of the Ulnar nerve, and throw it towards the fingers.

c. Divide the Median nerve at the lower border of the Annular ligament, and bring it also over the fingers, cutting through its branches to the muscles of the thumb and two outer Lumbrical muscles.

d. Cut through the origin of the Flexor brevis minimi digiti muscle from the Annular ligament and Unciform process, and throw it forwards. Its nerve from the Deep branch of the Ulnar will be divided.

e. Remove the central portion of the Anterior Annular ligament with the portion of the tendon of the Palmaris longus muscle which passes over it. f. Cut through the tendons of the Flexor sublimis digitorum muscle, and throw them towards their respective fingers. Beneath the Annular ligament they will be found to be arranged in pairs, the two to the middle and ring fingers being superficial to the other two.

There will now be exposed— 1. The Adductor minimi digiti muscle, beneath the Flexor brevis minimi digiti muscle.

2. The tendons of the Flexor profundus digitorum muscle, passing into the Digital sheaths beneath the Flexor snblimis tendons.

3. The Lnmbricales muscles more fully. The two innermost will be found arising from the contiguous sides of the tendons of the little, ring, and middle fingers. The two outermost from the Radial sides of the tendons of the middle and index fingers respectively.

4. Further portions of the Profunda branches of the Ulnar artery and nerve. Two slender twigs from this portion of the nerve are traceable to the two innermost Lumbricales muscles.

V

a. Divide the tendons of the Flexor profundus digitorum muscle, and throw them towards the fingers with the Lumbricales muscles attached. The nerves to the two innermost of these latter muscles from the Deep branch of the Ulnar will be torn through.

b. Divide the origin of the Adductor minimi digiti from the Unciform process and Annular ligament, and turn the muscle inwards. Its nerve from the Deep branch of the Ulnar will be divided. There will now be exposed—

1. The Interossei muscles of the third and fourth spaces, a Palmar and Dorsal in each, the former on the Radial side of the latter. These muscles are covered by their fascia.

2. The Adductor pollicis muscle more fully, arising from the anterior two thirds of the Metacarpal bone of the middle finger, and passing outwards to the thumb. It hides the Palmar and Dorsal Interossei of the second space, except at their anterior ends.

8. The inner head of the Flexor brevis pollicis muscle, arising from the Trapezoid bone, the Os Magnum, the base of the third Metacarpal bone, and the sheath of the Flexor carpi radialis tendon. It passes outwards to the thumb parallel with the upper border of the immediately preceding muscle.

4. The tendon of the Flexor longus pollicis muscle between the two heads of the short Flexor.

5. The greater part of the Deep Palmar arch, i.e., the Deep branch of the Ulnar artery, is seen to join the Radial.

6. The Deep branch of the Ulnar nerve is seen accompanying the corresponding branch of the artery, and ending in branches to the Adductor pollicis and the inner head of the Flexor brevis pollicis. Its twig to the Abductor minimi digiti muscle may be traced, but those to the Flexor brevis and the Adductor minimi digiti muscles are divided. Offsets to all the Interossei muscles may be found.

VI

To complete the dissection—

Remove the inner head of the Flexor brevis pollicis muscle from its origin, and throw it towards the thumb. Its nerves will be divided. This will expose—

1. The upper portions of the Palmar and Dorsal Interossei of the second space.

2. A further portion of the Abductor indicis muscle, previously covered by the inner head of the Flexor brevis pollicis muscle.

3. The whole of the Deep Palmar arch, which will be found to be formed in this way. The Radial artery is seen entering the palm at the back of the first interosseous space, between the two heads of origin.