carpi pollicis, and turns upwards, under cover of the anconeus muscle, to reach the posterior aspect of the outer condyle of the humerus. The anconeus should be detached

from its origin and

thrown inwards, in

brachial artery.

order that the artery

superior profunda.

anterior branch.

posterior branch.
nutrient.

inferior profunda.

anastomotica.

anterior branch.
posterior branch.

radial recurrent.
anterior ulnar recurrent.

posterior ulnar recurrent.
interosseous recurrent.
radial artery.

ulnar artery.

The

may be traced to its termination. interosseous recurrent artery will then be seen to end by anastomosing with the posterior terminal branch of the superior profunda artery.

The Anastomosis around the elbowjoint should now be reviewed as a whole. A distinct inosculation will be found to take place upon both the anterior and posterior aspect of each condyle of the humerus. Behind the external condyle the posterior interosseous recurrent joins the posterior branch of the superior profunda: in front of the same condyle the anterior branch of the superior pro

funda communicates with the radial recurrent. On the inner side of the joint the anterior and posterior ulnar

recurrent arteries ascend respectively in front of and behind the internal condyle, and anastomose, the former with the anterior branch of the anastomotic, and the latter with the posterior branch of the anastomotic and the inferior profunda.

In this sketch of the anastomosis around the elbowjoint only the leading inosculations are mentioned. Rich networks of fine vessels are formed over the olecranon process and the two condyles of the humerus. One very distinct and tolerably constant arch requires special mention. It is formed by a branch which crosses the posterior aspect of the humerus immediately above the olecranon fossa, and connects the posterior branch of the superior profunda with the posterior branch of the anastomotica.

The Posterior Interosseous Nerve (nervus interosseus dorsalis) is one of the two terminal branches of the musculo-spiral, and it reaches the back of the forearm by traversing the substance of the supinator brevis, and at the same time winding round the outer aspect of the shaft of the radius. It emerges from the supinator brevis a short distance above the artery of the same name, and is carried downwards between the superficial and deep muscles on the back of the forearm. Reaching the upper border of the extensor secundi internodii pollicis, it leaves the posterior interosseous artery, dips under cover of that muscle, and joins the anterior interosseous artery on the posterior aspect of the interosseous membrane. It will afterwards be traced to the back of the carpus, where it ends, under cover of the tendons of the extensor communis digitorum, in a gangliform enlargement.

The branches which spring from the posterior interosseous nerve in the forearm are given entirely to muscles. Before it pierces the supinator brevis it gives branches both to it and to the extensor carpi radialis brevior. After it appears on the back of the forearm it supplies the extensor communis digitorum, the extensor minimi digiti, the extensor carpi ulnaris, the three extensors of the thumb, and the extensor indicis. It therefore supplies all the muscles on the outer and back aspects of the forearm, with the exception of

the supinator radii longus and the extensor carpi radialis longior, which derive their nerve-supply directly from the musculo-spiral. The anconeus also derives its main nerve of supply from the musculo-spiral, but it also frequently obtains a second twig from the posterior interosseous

nerve.

Terminal Branch of the Anterior Interosseous Artery.— The terminal or perforating branch of the anterior interosseous artery is a vessel of some size. It appears through the interosseous membrane, about two inches or so above the lower end of the forearm. Accompanied by the posterior interosseous nerve, it runs downwards, under cover of the extensor secundi internodii pollicis, and ends on the back of the carpus by anastomosing with the posterior carpal arch and the posterior interosseous artery.

DORSAL ASPECT OF THE WRIST AND HAND.

Upon the dorsal aspect of the wrist and hand we have still to examine

1. The radial artery and its branches.
2. The posterior annular ligament.

3. The extensor tendons of the fingers.

Radial Artery. It is only a small portion of the radial artery that is seen in this dissection. At the lower end of the radius the vessel turns backwards below the styloid process, and upon the external lateral ligament of the radio-carpal joint. Having gained the dorsal aspect of the carpus, it runs downwards upon the scaphoid and trapezium, and finally disappears from view by turning forwards through the upper part of the first interosseous space, and between the heads of origin of the first dorsal interosseous muscle. In the palm it takes the chief share in the formation of the deep palmar arch.

While the radial artery rests on the external lateral ligament, it is deeply placed, and is crossed by the tendons.

of the extensor ossis metacarpi and the extensor primi internodii pollicis. On the carpus it lies nearer the surface, and is crossed obliquely by the third extensor tendon of the thumb, viz. the tendon of the extensor secundi internodii pollicis. It is accompanied by two venc comites and some fine filaments from the musculo-cutaneous nerve which twine around it.

The branches which spring from the radial artery in this part of its course are of small size. They are

1. The posterior radial carpal.
2. The first dorsal interosseous.

3. The two arteriæ dorsales pollicis.
4. The arteria dorsalis indicis.

The posterior radial carpal artery takes origin on the outer aspect of the wrist, and runs inwards upon the carpus, to join the corresponding carpal branch of the ulnar artery. The arch thus formed is placed under cover of the extensor tendons, and gives off two branches which run downwards in the third and fourth intermetacarpal intervals. They are termed the second and third dorsal interosseous arteries.

The first dorsal interosseous artery arises, as a rule, from the radial trunk, although not infrequently it may be seen to spring from the posterior carpal arch. It extends downwards in the second intermetacarpal interval.

The three dorsal interosseous arteries are brought into connection with the arteries in the palm by communicating branches. They are joined by the three perforating twigs of the deep palmar arch. These make their appearance on the dorsum between the heads of the three inner dorsal interosseous muscles. Further, at the lower ends of the interosseous spaces the dorsal interosseous arteries usually send inferior perforating branches to join the corresponding digital arteries in the palm.

The two dorsal arteries of the thumb run downwards upon either side of that digit.

The dorsal artery of the index is distributed on the radial side of the index.

Posterior Annular Ligament. This has been seen to be an aponeurotic band which stretches obliquely across the wrist. It is merely a thickened portion of the deep fascia, and its attachments are so arranged that it does not interfere with the free movement of the radius and hand during pronation and supination. On the outer side it is fixed to the outer margin of the lower end of the radius, whilst on the inner side it is attached to the cuneiform and pisiform bones, and also to the palmar fascia. In the case of the anterior annular ligament one large compartment, or tunnel, is formed for the flexor tendons; not so in the case of the posterior annular ligament. Partitions or processes proceed from its deep surface, and these are attached to the ridges on the dorsal aspect of the lower end of the radius, so as to form a series of six bridges or compartments for the tendons. Each of these is lined by a special synovial sheath, to facilitate the play of the tendons within it. The different compartments may now be successively opened up, so that the arrangement of the tendons with reference to the posterior annular ligament may be studied.

The first compartment is placed on the outer side of the base of the styloid process of the radius, and corresponds with the broad oblique groove which is present in this part of the bone. It contains two tendons, viz. the tendons of the extensor ossis metacarpi and the extensor primi internodii pollicis. The second compartment corresponds with the outermost groove on the dorsal aspect of the radius. This is broad and shallow, and it holds the tendons of the extensor carpi radialis longior, and of the extensor carpi radialis brevior. The third compartment is formed over the narrow deep intermediate groove on the back of the lower end of the radius, and through it the tendon of the extensor secundi internodii pollicis passes obliquely. The fourth compartment is placed over the wide shallow groove which marks the inner part of the dorsal aspect of the lower end of the radius. It is traversed by five tendons, viz. the four tendons of the