is sometimes much reduced in size, and frequently more or less completely incorporated with the opponens. Its nerve supply comes from the deep branch of the ulnar

nerve.

The opponens minimi digiti (opponens digiti quinti) arises from the annular ligament, and the hook of the unciform bone and its fibres spread out to obtain insertion into the entire length of the ulnar margin of the metacarpal bone of the little finger. The deep branch of the ulnar gives it

its nerve of supply.

The Deep Branch of the Ulnar Nerve springs from the parent trunk on the anterior aspect of the annular ligament, and gives off a branch which supplies the three short muscles of the little finger. Accompanied by the deep branch of the ulnar artery, it then sinks into the interval between the abductor and flexor brevis minimi digiti, and turns outwards across the palm under cover of the flexor tendons. Near the radial border of the palm the deep branch of the ulnar nerve breaks up into terminal twigs, which supply the adductor transversus pollicis, the adductor obliquus pollicis, and the first dorsal interosseous muscle. In its course across the palm it lies along the concavity or upper border of the deep palmar arch, and sends three fine branches forwards in front of the three interosseous spaces. These supply the interosseous muscles in those spaces, while the two inner also give branches to the deep surfaces of the two inner lumbrical muscles.1

The deep branch of the ulnar may, therefore, be said to supply all the muscles of the palm which lie to the inner side of the tendon of the flexor longus pollicis, whilst the median supplies the three muscles which lie to the outer side of that tendon. There are two exceptions to this generalisation, viz., the two outer lumbrical muscles, which lie upon the inner side of the tendon, and are yet supplied by the median nerve.

1 The third lumbrical has frequently a double nerve supply, as it is not uncommon to find a second twig from the median entering its superficial aspect.

Deep Palmar Arch (arcus volaris profundus).-The artery which takes the chief part in the formation of this arch is the radial. This vessel enters the palm, by coming forwards through the upper part of the first interosseous space between the two heads of the first dorsal interosseous muscle. In the present state of the dissection it makes its appearance between the contiguous margins of the adductor obliquus and adductor transversus pollicis. It runs inwards upon the interossei muscles and the metacarpal bones immediately below their bases. As it approaches the fifth metacarpal bone it is joined by the deep branch of the ulnar artery, and in this manner the deep palmar arch is completed.

The deep palmar arch does not show so strong a curve as the superficial arch, and it is placed at a higher level in the palm. It is closely accompanied by the deep branch of the ulnar nerve; and is separated from the superficial palmar arch by the group of flexor tendons, the lumbrical muscles, the branches of the median nerve which occupy the middle compartment of the palm, and also at its inner part by the flexor brevis minimi digiti, under which the deep branch of the ulnar artery passes to join the radial.

The branches which spring from the deep palmar arch are: (1) the recurrent-a few small twigs which run upwards in front of the carpus to anastomose with branches of the anterior carpal arch; (2) superior perforating, which pass backwards in the upper parts of the interosseous spaces to anastomose with the dorsal interosseous arteries; and (3) the palmar interosseous— three in number-which pass forwards in front of the interosseous spaces and unite near the roots of the fingers, with the corresponding digital arteries from the superficial palmar arch. Sometimes one or more of these branches enlarge and take the place of the corresponding digital arteries.

Dissection. To bring the arteria radialis indicis and the arteria princeps pollicis into view, the adductor transversus, and the

adductor obliquus pollicis must be detached from their origins and turned outwards. The radial artery is now seen coming forwards between the two heads of the first dorsal interosseous muscle.

as it

Arteria Radialis Indicis, and Arteria Princeps Pollicis. These arteries spring from the radial proceeds forwards between the first and second metacarpal bones.

The arteria radialis indicis runs downwards between the adductor transversus pollicis and the first dorsal interosseous muscle to the radial border of the index, along which it proceeds as its outer collateral branch.

The arteria princeps pollicis takes a course downwards and outwards under cover of the adductor obliquus pollicis, and gains the front of the metacarpal bone of the thumb. Here it lies behind the tendon of the flexor longus pollicis, and divides into the two collateral branches of the thumb. These branches make their appearance, in the interval, between the adductor obliquus and the superficial head of the flexor brevis pollicis, and are carried forward on either side of the tendon of the long flexor.

Surgical Anatomy of the Palm and Fingers.-When an abscess forms in the middle compartment of the palm early surgical interference is urgently called for. The dense palmar fascia effectually prevents the passage of the pus forwards, whilst an easy route upwards into the forearm is offered to it by the open carpal tunnel, through which the flexor tendons enter the palm. It is absolutely necessary, therefore, that before this can occur the surgeon should make an opening in the palm by means of which the pus can escape. In making such an incision it is a matter of the utmost importance to bear in mind the position of the various vessels which occupy the middle compartment of the palm. As we have stated, the level to which the superficial palmar arch descends can be indicated by drawing a line transversely across the palm from the lower margin of the outstretched thumb. The deep palmar arch lies half an inch higher. The digital arteries, which spring from the convexity of the superficial arch, run in a line with the clefts between the fingers. An incision, therefore, which is made below the superficial arch, and in a direction corresponding to the central line of one of the fingers, may be considered free from danger in so far as the vessels are concerned.

The loose synovial sheath which envelops the flexor tendons as they pass behind the anterior annular ligament has been noticed to extend upwards into the lower part of the forearm, and downwards into the palm. When this is attacked by inflammatory action it is apt to become distended with fluid (thecal ganglion) and the anatomical arrangement of parts at once offers an explanation of the appearance which is presented. There is a bulging in the palm, and a bulging in the lower part of the forearm, but no swelling at all at the wrist. Here the dense annular ligament resists the expansion of the synovial sheath, and an hour-glass constriction is evident at this point.

The fingers are very subject to an inflammatory process, termed whitlow, and, in connection with this, it is essential to remember that the flexor fibrous sheath ends on the base of the distal phalanx in each digit. When the whitlow occurs below this, in the pulp of the finger, the vitality of the distal part of the ungual phalanx is endangered, but the flexor tendons may be regarded as being tolerably safe. When the inflammation occurs above this, and involves the flexor sheath, as it generally does, sloughing of the tendons is to be apprehended, unless an immediate opening is made. And no slight superficial incision will suffice. The knife must be carried backwards in the centre of the finger, so as to freely lay open the sheath containing the tendons. Early interference in cases of whitlow of the thumb and little finger is even more urgently required than in the case of the other three digits, because, as we have seen, the digital synovial sheaths of the former are, as a rule, offshoots from the great carpal bursa, and offer a ready means for the upward extension of the inflammatory action.

Every amputation of the fingers above the insertion of the tendons of the flexor profundus involves the opening of the flexor sheaths, and this no doubt explains the occasional occurrence of palmar trouble after operations of this kind. The open tubes offer a ready passage, by means of which septic material may travel upwards into the palm, and, in the case of the thumb and little finger, into the carpal tunnel and lower part of the forearm.

BACK AND OUTER BORDER OF THE FOREARM.

The cutaneous nerves and vessels in this region have already been studied. The parts which still require to be examined are:

VOL. I.-9

1. The deep fascia.

2. The supinator and extensor muscles.

3. The posterior interosseous artery.

4. The perforating or terminal branch of the anterior interosseous artery.

5. The posterior interosseous nerve.

Deep Fascia.-The deep fascia on the posterior aspect of the forearm is stronger than that which clothes it in front. At the elbow it is firmly attached to the condyles of the humerus and the olecranon process, and it receives a reinforcement of fibres from the tendon of the triceps muscle. Here also it affords origin to the extensor muscles, and sends strong septa between them. At the wrist a thickened band-the posterior annular ligament— is developed in connection with it. This can readily be distinguished from the thinner portions of the fascia with which it is continuous above and below, and it will be observed to stretch obliquely from the styloid process of the radius inwards and downwards across the wrist to the inner side of the carpus.

Dissection. The deep fascia should now be removed, but that portion of it near the elbow, which gives origin to the subjacent muscles, should be left in place. The posterior annular ligament should also be artificially separated from it, and retained in situ.

Superficial Muscles.-The muscles in this region consist of a superficial and a deep group. The superficial muscles, as we proceed from the outer to the inner border of the forearm, are:-the supinator longus, the extensor carpi radialis longior, the extensor carpi radialis brevior, the extensor communis digitorum, the extensor minimi digiti, the extensor carpi ulnaris, and the anconeus. This group therefore comprises one supinator, three extensors of the wrist, two extensors of the fingers, and a feeble extensor of the forearm at the elbow-joint, viz., the anconeus. In the lower part of the forearm the extensor communis digitorum is separated from the extensor carpi radialis brevior by a narrow interval, and in this appear two muscles belonging to the deep group. These turn round the outer border of the forearm upon the surface of the radial extensors of the wrist, and end